Place I used to contract had a knee-high pile of Compaq 386 laptops in the radio system engineers' office. When I offered to surplus them and get them out of the way they almost attacked me. They had a half million dollar radio tower that used a bleeding-edge control system when it was first installed. The manufacturer got bought out and the new owner didn't support the thing any more. The control system software would ONLY run on a 386 running DOS 3, nothing else, and that pile of laptops were their backup tower controllers. The last time I was there I noticed the pile was gone so they must have upgraded the tower.
There are a lot of expensive legacy systems that rely on outdated operating systems to function. I personally have encountered MRI machines, an access control system, metal lathes, a sawmill, and a factory floor automation system that will not run on anything higher than NT 4.0, a company isn't going to throw away a multimillion dollar automated lathe just because the OS is outdated (or at least they shouldn't). The security model in Server 2008 broke a lot of software, for companies that aren't on the continual upgrade treadmill Server 2003 is going to be around for quite some time.