PS3 - yes and no.
On a PS3, I don't believe it has the attachments for a simple USB drive. It does, however, accept normal internal HDDs as far as I know (the real big large ones).
The 360 on the other hand, does accept USB HDDs readily, but they won't interact with the X360 as readily as an MS unit. It's basically a storage device and not an intergrated storage solution (ie, you'd pretty much always have to select storage drive>USB drive>save rather than just 1 click).
For HDDs: The issue is, aside from flash memory, creating an actual HDD is expensive. There is a minimum cost a company will incur (around $30-$40) to make a hard drive, due to raw materials. MS, Sony or anyone, cannot avoid that price. The issue is that from a 20gb model to 120gb model, the price increase is very very small vs. the initial cost to build a HDD.
I bought a 80gb HDD (standard) a few months ago @ $50. To buy a 160gb, it would cost $70 at the same timeframe, or $120 or so for a 250 or even 320.
Back from the dead, I'm afraid.
