I am willing to bet that if you built a PS2 out of the best parts money could buy, and ran a disc non-stop, that the one standing vertical would shit the bed way before the horizontal.
I don't care what anyone says- I don't believe that this machine is built to be played on it's side.
I just dont think that a compact disc's rotation would be the same that way, and I would believe there would have to be more errors from a sideways cd tray.
the fact that many ps2's die standing up vertically and horizontally just shows what a cheaply made piece of crap it is.

willie