I did a bit more research, and finally came up with a gaming forum somewhere where someone was talking about how much he hated that the PS3 has underscan built in, so that no matter what game you're playing (no mention of BDs or DVDs), there's black bars all around. I assume that that makes it great for HDTVs that do have overscan (like mine), but it sucks if your TV has no overscan, cos then you get black bars all around.
I suppose it makes sense since Sony makes (a lot of?) HDTVs with overscan. Still, to have a forced 5% underscan for everything seems a little TOO focused on your own brand.
Anyway, looks like the kid was right!
cheers,
supervij