Thats not exactly how it works. The pipes are built to support temperatures well above their evaporating point. All high end PC's use this. My Alienware uses this.
Well, Xbox 360 has a manual and it specifically says to give Xbox 360 "room for oxygen" where the worse place to have it is in a enclosed cabinet. Want me to scan it for reference?
PS3 would have simular heat debates and would likely to have the same description in it's own manual word for word.
yer, im pretty sure that the PS3 will have this warning written down somewhere, i have my 360 on top of a dvd player, below a glass shelf and its fine lol!