Given the same generation technology, a higher-capacity drive will have more platters, which means more mass to spin, which means more heat generated.

A theoretical possibility no doubt. But there are no practical examples where larger drives pose a problem even in small enclosures of a laptop.

My 250 Gig WD Scorpio runs quieter/cooler than the 160 Gig Samsung (Apple OEM) that it replaced.

It's a scientific fact.

A 100GB drive and a 200GB drive from the same model cycle by the same manufacturer in the same year will have different heat output.

Obviously there are other factors at play too, I am just pointing out the baseline.

You are talking about two drives that are different generations of technology.

in theory, yes. But i think those manufacturers sure know about the heat issue, or else they goin' bankrupt soon. It's common sense that they will have some kind of solution or whatever to that. In my opinion, i'm sure the 200Gb hdd microchip itself is different than the 100Gb drive, even it's same generation. It's not likely that they so dumb, by just changing the disc inside hdd to make the capacity big.

So, i still think there's likely no heat problem even you have a bigger drive