Well Dell could stockpile the licenses and then resell them off I would imagine. But Microsot won't be selling anymore OEM and Retailer license after June 30th. The other thing that happened is that Micorosoft added five additional year to windows XP Home and Media Center lines I believe.
You can see a little bit more on this at this blog.
MICROSOFT SUPPORT LIFECYCLE BLOG : What?s happening to Windows XP on June 30th?