The thing is, it's still fun, but it also becomes a chore pushing it higher and higher... I'm now always playing at 1.1M and the results are more frustrating.
Dave nailed something here.
I am of the belief that the kill screeners list will continue to grow considerably, as will (to a lesser extent) the million-point list, but when it comes to 1.1, I don't see more than four or five more people out of the current crop of known players who will ever push their DK game there (Dave being one of them, probably Phil T, et al.)
As for 1.15+, I can see Hank, Vincent, and Jeff all joining Dean at that level, but it would not surprise me if nobody except those four specific people ever does it.
What Dave said here is exactly the reason why I believe this. When you're squeezing the game for every last drop, it just starts getting really tedious to play.
Every DK "achievement" calls for a more and more concentrated degree of (for lack of a better term) obsessiveness, and 1.1 and higher is demanding in a way that getting a kill screen or a million just isn't. You're not learning anymore (not very much at least), so that aspect is gone, there are no more breakthroughs or new personal bests, etc. The fun and novelty is gone. Now you're just grinding, grinding, grinding at it until the right game comes together.
Plus, as more people hit 1.1 or 1.15 (or whatever) it naturally dis-incentivizes doing it. How cool to be the first or second to do something, but pushing and pushing just to be the seventh or whatever? Not so much.
I can tell you right now that I will never go for 1.1! The things you have to do, and the lack of bad luck you have to wait for in order to complete a 1.1 game is not interesting to me.
I'm not saying that those who push for 1.1 and beyond are wrong, but it calls for a very particular psychological outlook and approach. Dean, for example, enjoys playing the first 4 levels over and over for 2 hours in order to get a good start. There's nothing wrong with that, more power to him, but that would make me miserable. The maxout approach is definitely not for me, and not for a lot of players who otherwise enjoy the game. I think many of us would say that if we can get through all the screens and flip the score over, awesome. That's enough for us.