Flight Simulator X Activation

I picked up Flight Simulator X a while ago, installed it and Activated it.  This hands Microsoft my Product Key, which they validate, and then unlocks the software. 

I recently installed Windows Vista, and when I reinstalled Flight Simulator and went to Activate it, I assumed I'd be on the phone to Microsoft begging them to let me play my game - but instead the activation succeeded, no questions asked.

I don't know why, but I'm happy that it did.  Maybe they're remembering the IP address of the previous activation, or the Mac address.. however they're doing it, in my case, it worked out just fine.