I didn't see your edit until just now… I might comment later but to be honest, for the most part I agree with you. I'm comparing similarities between gearing in PvE to gearing in PvP to refute that PvP ruins PvE. It does not, in any way. It's very separate and while there is some cross bleeding, for the most part they can be played independently of each other.
A player can do both, but you never have and never will gear in PvP to be a top raider, and you will never gear in PvE to be a top PvP'er.
Maybe more later :)
Response to your edit… I'll go by your numbers.
1) That's not entirely accurate… sure you might have a rudimentary understanding of what each class is capable of, but you don't know what spec they are, what gear they are wearing, or how they play their class. Players can, and do, pull tricks on you because you generally don't know what to expect. The players who do the best in PvP have tactics that other players haven't planned for, and they are also capable of reacting fast enough to counter the other team's tactics. By contrast, in PvE it's a comparatively more simple matter of throwing yourself at a boss until you do learn that encounter. What makes it easier is that things aren't going to change. Whatever caused your wipe last fight is generally static and once you see it, you can figure out how to counter it and you now know it's coming. Almost every boss in WoW is completely predictable… to the point where scripted mods are written to tell you exactly what is happening when. The only exception is a few small cases where it is random for drop placement… the first example I can think of that most people will have seen is prince.
In a PvP match, you generally get one shot. You win, or you lose, then you move on to another match up. The only way PvE could compare to this is if every time you wiped on a boss, the next time you fought it there would be something else quite different that you face. This isn't the case.
2) No, the boss will never grow lazy or complacent, or have an off day, but that's my point. It never changes, it's the same every time. You have to remember that in PvP, there are two thinking and reasoning entities against eachother, so if one has an off-day, another wins. If you wipe on a boss, there is only a loser… the boss doesn't win, it doesn't care. It gains nothing, doesn't progress, it's the same. If you're to say that you can't overwhelm a boss with sheer numbers, the same applies to PvP (not counting world-pvp) as matchups are equal. If you disagree, then it's a valid statement to say that individual components of a boss are overwhelmed with sheer numbers, which degrades the argument entirely. You can also outgear encounters… bosses are often skipped to be done later when people are better geared. Many new instances aren't completely linear and contain difficult, yet optional bosses. Naxx is an example of this… you're free to start and complete wing you like. It's quite possible to farm certain wings until gear is bloated and it is much easier to fight other bosses in another wing. I'll admit that's kind of a skewed point because that's pretty much how raid progression works, but I find your comparison to PvP equally as skewed so I figured I'd toss it out there.
With regards to penalty… what's the death penalty in PvE? You pay a bit of gold, then you get right back on the horse and try again. No real loss, and given the nature of a PvE encounter, sheer perseverance and gear will surmount 90% of the odds against you. In PvP, failure results in low standing. Consistent failure results in falling behind, which means further failure. If you fail at PvE and take a year to down one boss, the next boss is still one small step above the one you just beat. If you fail at PvP and take a year to complete your first set, you are much farther behind as the rest of the competition has surpassed you greatly in gear and your encounters only become more difficult. I guess what I'm trying to say is, in PvE you have control over what you face, in PvP you don't.
Last point on this one… falling behind other players in PvE generally means nothing. Yea if you're the first to down something world-wide, people might, maybe, possibly, remember your guild name. If you're the second, a much smaller group knows, or even cares. If you're third? Nobody has any clue who you are. Past that it doesn't matter. You aren't going to have a harder time in PvE because someone else is doing better than you. If someone else does better than you in PvP, you suffer directly because you have to face those teams who are now better geared and more skilled.
3) PvE is static, predictable progression with unpredictable rewards. PvP is predictable rewards but unpredictable progression. However, in PvP you can catch up to the competition in comparatively little time to PvE. I see this as a gigantic flaw in PvE far more than any issue with the PvP system. There was too big a gap between new players coming in and Naxx players, to the point where anybody who didn't start raiding at day one found it extremely difficult to catch up. Most Naxx guilds wouldn't accept anybody without at least a good portion of AQ40 gear. It simply doesn't make sense to design a game this way… at least not if you want to attract new players. Again, a flaw in the PvE system.
What do you mean players never surprise you? Have you even PvP'd? You weren't surprised the first time a priest mind controlled you and threw you off a cliff, or zoned you out of the battleground? You weren't surprised when you were guarding a flag and 5 rogues popped out of stealth, destroyed you, and capped the flag? You weren't surprised when just as you were about to kill someone a healer who was heading in at full speed mounted just got there in time to heal them? You weren't surprised when some warrior quickly switched on a shield and spell-reflected that pyroblast? You weren't surprised (and utterly amazed) when a frost mage kited you into oblivion after you got them down to 10% health and you just couldn't quite get there for the finisher?
Those are just a small subset of the things I've experienced in PvP that I never would have seen coming or expected, and even if I've seen them you never know when they are coming again. PvP is full of variety. The only time you get variety in PvE is when Blizzard finally gets around to designing a new instance, and then it's just a matter of throwing yourself at the content until you learn that and get bored with it too.
Please note, that last comment is pretty much the negative end of the spectrum… I actually do enjoy PvE and it is fun learning the new encounters. However, once you learn them they get stale, whereas I'm finding myself being pulled more and more towards PvP simply because of the unpredictability.