According to the Steam hardware survey it is already at less than 10% - it’s around 6% and declining. 64-bit XP has 0.33% of the total share (and is obviously also declining). You’ve seen this yourself and quoted it in your own stats. XP is not 29% of the market and if you’d looked further than the little chart on the Wikipedia page you probably got that statistic from, you might have noticed a few important things:
A) Very significant numbers of those machines will be things like ATMs, which usually run on XP (19 in every 20 ATMs are a Windows XP box). There are millions of ATMs in the world, and they’re not going to be buying your games.
B) The same Wikipedia article cites that “25–35% of all Windows XP machines are illegal.”. These people are also unlikely to buy your games.
C) The same Wikipedia article cites that Wikimedia’s own estimated count for XP users (based on those browsing the site) is way down at 7%, slightly higher than the Steam estimate, which isn’t surprising because it’s a popular web page.
D) You’re still missing the point that the majority of XP boxes that are still in use are not going to be owned by people who have hardware to run your games. Windows XP ceased being shipped on the majority of home machines in early 2007; or shortly after previous gen consoles and the Geforce 8 series became available. That’s a full eight hardware generations behind.
Windows XP is a dying operating system used by a few hardcore hangers-on and people on antiquated boxes that don’t use their machine for anything other than basic tasks, so won’t upgrade. Doing the hard work to cater for it is absolutely bonkers.