Furthermore, o/s version and the age of the hardware it's running on, tend to be closely linked, as most people (and businesses) don't perform major version upgrades on hardware, they replace hardware with new versions loaded.
But consider that because of the problems with Vista, many venders were selling new computers with XP on them up till 2008-2009. For many users those machines still have several years on their life (average 5-6 years for a business use machine (emails, word processing and such)).
@Zippy - My particular situation has closer to 80% xp installs. But I am not arguing for my situation. Microsoft cannot made decisions based off of me. I am saying that the market share of XP is still so high. And the damage caused to XP by this .NET release is extreme. To do that to such a large amount of users (and by extension developers) is crazy.
@spivonious We were doing that until about a year ago. Happily we have stopped now. However, it will still be several years before we get "off" xp.
@Kettch - I never thought of it as easy. But if it applies to a fourth of the market, it is the right thing to do.