Although Microsoft, retailers can keep selling it as long as they have copies.
Perhaps as a result of its potentially impending scarcity, XP is near the top of Amazon.com's software list, with the full version of XP Home at No. 15 and the full version of XP Pro at No. 21.
The highest ranked Vista edition doesn't crack the top 25, although it does come on nearly all new PCs these days so most people don't need a boxed copy.
For those keeping score, Apple's Mac OS X Leopard is No. 7 on the software list, while the highest ranking Vista version is the update version of Windows Vista Home Premium, at No. 41.
On the bright side for Redmond, Office Home and Student for Windows is No. 1 and the Mac edition of Office Home and Student is No. 3.
For those still looking to get their hands on XP, it doesn't seem like it's all that hard to find. Best Buy had it listed in several different flavors online and noted that it's also available in most stores. Staples, Office Depot, Circuit City, and OfficeMax all listed at least one version of XP on their Web sites as well.