I'm not sure about this, but I think what's happening is the game is consuming all the virtual memory and Windows is not freeing it up after the game closes. I think it's a Windows problem and not something that's necessarily the games fault. I used to experience this on an older machine with less memory, but my new machine has 2GB of physical memory and doesn't exhibit the problem. That doesn't really help you, but at least it gives you a possible reason why you have to restart.
This is what I thought as well, but don't know how to stop it. I do have only 1 gig of RAM, but according to Windows, nothing is hogging my virutal memory after I exit. Not that Windows policing itself means much.
And yes Windows is a pig but no other game does it, so doesn't that imply it's galciv's fault?