XP is over 12 years old, that's one hell of a *free* long term support package.
How long it has been since a company sold a product to their first customer is irrelevant. What matters is how long it has been since they sold the product to me. Microsoft stopped retail and OEM sales of XP in June 2008, which was shortly after Vista SP1 was released and most if it's problems had been fixed, and a bit more than a year before Windows 7 was released. Those customers got just shy of 6 years of support, which is still pretty darn good. In comparison, Ubuntu offers 3 years of support for an LTS release after it's replacement comes out, and OS X tends to be about the same. However, those both offer free or cheap upgrades so a shorter support cycle is at least somewhat justified.
For corporate customers, the support provided by a RedHat subscription is entirely comparable. No moderately sized company can get away with using OEM/retail licenses of Windows/Office; they all pay some sort of subscription to MS. RHEL 5 will be supported for just over 6 years after RHEL 6 came out. RHEL 2-4 were each supported for 5 to 5.5 years after their successor. Both MS and RH have extended support for critical security bugs beyond that, but both cost extra money. Recent Solaris releases are as good or better (depending which support phases you consider comparable).
So for corporate users, XP's support duration was reasonable and in line with the rest of the industry. For consumers it was much better for people who have to stick with older OSes for compatibility, and hard to compare once you start considering free upgrades (is an OS X point release comparable to a windows SP release or an OS release, etc).