I wonder if you're citing end of sales with OS X "died" dates, not end of support. End of support (updates, etc.) is different from no longer offering for sale.
For example, OS X 10.7 still seems to get security updates. Going by end of sales, Windows XP "died" June 2008.
Ars Technica just did an article suggesting that 10.6 isn't getting security updates anymore. The same article says 10.7 just got an update too.
So your figures for OS X might be exaggerated. That said, you're correct that XP has gotten unusually long support.