Kinda makes you ask, "Why is there more than one price for Windows?" once again, doesn't it?
Good question hellwig, my guess is no, because the OEM versions are far cheaper than the retail ones, and with most computer purchases you don't have the original install disk anyway; you at best have a 'repair' disk, which isn't the same. The difference though is minor, it is just a matter of running out to pick up a new upgrade DVD (or waiting to get one from an etailer) or already having it on a disk in your home/office.
It has long been the practice of hobbyists such as myself to recommend a fresh install over an upgrade install anyway; if you format the hard drive and start from scratch, you start from a clean system, which will run better than upgrading the old one. Any files you want to save can be put on a CD or DVD and loaded back after the new install. This isn't the problem it used to be, but still is a better option for an upgrade - and still a MUST for a re-install. It doesn't matter whether or not you use the same installation disk, the process is the same, and you'll pay for the upgrade, just the same.