lowyhong: Again, I can't say for certain that Steam doesn't test out their games before releasing them...
klaymen: Games like Commandos or Jagged Alliance 2 showed that if they do test their games, the test looks like:
*employee runs the game*
*employee gets to the main menu*
*employee marks the game as working*
*employee moves to next game to test*
Maybe it's ironic but it's probably the truth. Here's the games I had problems with:
Two Worlds: refused to run because it didn't add registration info in the registry
Commandos: ran too fast
Aliens vs Predator: too many problems to name
Arx Fatalis: too many problems to name
Beyond Good & Evil: serious graphic problems + speed issues
Dracula: Origins: serious mouse issues for anyone who uses a Logitech mouse
Doom I & II: crucial files were deleted + bad DOSBox settings (goes for most DOSbox games)
Quake I: CD music was thrown out
Jagged Alliance 2: some serious bugs
Hexen II: CD music thrown out
There's probably more but these are the ones I remember - I do own 140 games on Steam. Nearly all old games are just not fixed and contain all the errors that they have on modern systems.