To be fair. That figure is irrelevent. The only relevent figure is how many of his customer still using WinXP and won't upgrade to a newer OS.
And for Vaccano, since Microsoft did nothing from preventing you to use VS2010 to develop for WinXP, I think if you're pinned by customer demand to still develop for WinXP, you shouldn't complain.
See VB6 users continue to complain they can't get workable multithread solution even if they continue to pay for MSDN subscription.
And, except those syntax sugars, name one thing that is missing in .NET v4.0 that'll affect your ability to build solutions to show it's a big deal for you.