Quite a while back there was a poll here on EnWorld, a similar one on RPGNet and another on a site I forget, which asked which edition people preferred.
The editions were broken down into BX or related, AD&D, 2E, 3E/3.5/Pathfinder, 4E, Next (roughly, I forget the exact breakdown).
I found two things interesting.
3E/3.5/Pathfinder roughly had 25%
4E roughly had 25%
All older editions (and clones) shared 50% of the market
The older editions are fairly compatible, for the most part, so I found it very interesting that a large part of the market enjoyed these older games (game designs).
You could call it nostalgia, or perhaps they just worked fine.
I wish I could get more data on this.