It's strange that gamism is the least popular one for D&D.
Agreed. My impression of these boards is that some version of Gygaxian play - "skilled play" with a fairly robust simulatinionst chassis underpinning it - is the most common approach. And 3E tended to reinforce this approach, I think. (Though seems to be have been easily drifted in more simulationist directions.)
Methinks gamism still has an unfortunate stigma.
Agreed. Also, on these boards by "gamist" most people mean something like "metagame mechanics heavy" rather than "step on up".
Since 4e fairly succeeded at balance it would probably be the most Gamist version of D&D. Might be hard to claim that 1e and 2e were more G than N & S.
I won't comment on 2nd ed, but have a read of the last few pages (before the appendices) of Gygax's PHB. It would be harder to find a clearer gamist manifesto than Gygax's advocacy of, and explanation of, "skilled D&D play". His DMG is also written with the same sort of playstyle firmly in mind.
I think of 4e as Dramatist, rather than Gamist, because the point of a lot of the rules structure is to simulate the "perfect D&D game", rather than to provide a foundation for competition per se.
For example in 4e combat, PCs are like 100 to 1 favorites against equal level monsters. The design of the system isn't really about challenging the players (this is not to say that it's completely without challenge, or that you can't make it more difficult; we're talking about priorities here). It's more about trying to simulate the "perfect battle" where the players are getting womped, almost to defeat, but then rally and win the day. Again and again.
And it does that admirably! If we take that as the design goal, then it's actually really, really smart at doing this. My disagreement would be at the level of the design goal, not the implementation.
I think the designers seriously overestimated how much fun it is to have the "perfect" battle/adventure/campaign again and again. They badly missed something here.
I agree with what you say about those features of 4e that militate against gamism. I would add to that it's XP award and treasure acquisition guidelines. But [MENTION=27160]Balesir[/MENTION] has made clear to me that there is a different sort of gamism that 4e supports well (I call it "light gamism") - showing off to your fellow players by doing cool things with your PC (that reflect cleverness of build and of play), using the "perfectly balanced" situations that the GM has constructed as a reliable arena in which to do this showing off.
I'm not sure if this is what the designers had in mind or not, but it seems to me a very straightforward application of the game (I'm not even sure I'd call it drifting).
I've also found that 4e is very easily drifted to narrativist play (basically, just use the guidelines from a game like Burning Wheel to guide you in introducing story elements into encounters, and use the guidelines from HeroWars/Quest and Maelstrom Storytelling to frame skill challenges, and use the guidelines from those games plus BW to make decisions about the consequences of successful or failed checks in a skil challenge).
Provided that you enjoy the gonzo fantasy tropes of D&D (I do) and want the thematic content of your game to be the sort of stuff that those tropes can support (again, I do - we're not talking about My Life With Master at my table!) then 4e does narrativism fairly well in my experience.
I use D&D when I seek gamist play. I want dangerous exploration, tactical combat and hard negotiations; I want to be challenged in various ways during play and try hard to overcome what the DM throws in my way.
In my experience, D&D was never good at supporting narrativist or simulationist play and I don't think it will change in the future. I use different games for this.
I think 4e can be easily drifted to a light narrativism in the way I've just described - it has a lot of thematically rich story elements (paragon paths, plenty of the classes, plenty of the monsters, etc) and the player-protagonising mechanics (in PC build and action resolution) to let the players rather than just the GM do stuff with these story elements.
I don't think earlier editions do narrativism at all well, because they're full of mecahnical systems that drag play out of the situation and into the exploration-heavy nitty-gritty of operational play. I regard 2nd ed as the poster child for mismatch between apparent aspirations for play and actual mechanics adopted by the game.
And as a long time Rolemaster player (a sim-heavy game that also is surprisingly easy to drift to narrativist play, in a way that superficially similar games like RQ are not), I don't understand at all the apparent attraction of 3E as a sim vehicle that I often see expressed on these boards.
That said, narrativist combat doesn't usually take 2 hours

Or, more properly, combat in "Story Now" games tends to go pretty fast compared to 3.x and 4E.
Except when you're playing narrativist 4e! Then combat is where the thematic action is.
If someone could link me to the relevant 26 page ENWorld discussion thread on the subject I'd appreciate it.
You asked for it!