Im sure there is no economic incentive for Microsoft to ship XP anymore. I'm also sure there is lots of PR incentive to stop shipping it. Why would Microsoft put themselves in the position of saying, "oh, our new OS isn't working so here, use the old one instead?"
I guess i need to route around ebay a bit and pick up a couple more XP licenses while i still can.
If you are serious about XP licenses, go to a large reseller like a Dell, pcconnection, etc and buy a corporate volume license. The beauty is you wind up with one PID that turns on each instance you install, and there is no need to activate on each installation. I also found that as we swapped out motherboards and hard drives, the lack of required activation was a huge plus.
It is also the honor system. If you buy 5 licenses, you are expected to honor that and not put it on more than 5 computers.
You save a few bucks and eliminate activation.
Now, the other side is, NEVER buy a single retail full version, always buy an upgrade. All you need is an old DVD with an older Windows version and you can install. Same generally true on Office, although I cannot speak to Office 2007 or Vista.