I don't mind good stuff floating to the surface eventually, I just hate it when games disappear from Steam. Why introduce Descent 1, 2, 3 only to have them removed a year later? I understand that there can be legal issues from time to time but shouldn't a big company such as Valve be able to find a certain solution for such problems?
Neverwinter Nights 2
Wolfenstein 2009 game
The original Prey
and a whole lot more...
Worst part is, once these games disappear from the store, the support for them disappears as well, even if you happen to already own them. So if it's a multiplayer game you can pretty much kiss it goodbye or start looking for workaround tactics...