I asked Sony about this back when I had to replace my original launch
PS2 with one of the latest ones a few months ago. On the launch PS2,
none of the vents are blocked as they were placed higher up. As
usual, Sony's CSRs were *completely* clueless and had no idea what I
was talking about. I gave up and have been running my PS2 with the
horizontal stand since September with those vents partially blocked
and have not had any sort of problem with my system.