Here's my take on 2.5 and 5GB hard drives. Apple won't be using the 2.5GB drives because it'll really cut into their margins (remember, the iPods are their money makers). Instead, Apple will use the 5GB models formatted as 4GB, as someone had already mentioned. In fact, it will behoove them to do so.
The rest of the computer industry already implements this practice anyways. AMD and Intel will downmarket a chip from, say, 2.8Ghz to 2.4Ghz if the market demands more 2.4Ghz chips. ATI will severe half of their rendering pipes (via software) just so there will be enough supply of the slower video card. Microsoft reformats 10GB hard drives to 8GB for their Xboxs.
So why can't Apple do the same? Certainly there's nothing in the iPod specifications that mention hard drive makers or rotation speeds. They can pop in a 5GB-turned-4GB hard drive and none would be the wiser (it's not like we're cracking open these things anyways). And having two hard drive suppliers are better than one. I know Hitachi said they are ramping up, but can you say "the IBM 3Ghz CPU Promise?"
An Apple iCamera? Probably won't happen either. The market is too crowded and the margins aren't that great unless they go 6MP or better. Hell, I can get a no-name 3MP digital camera for $80 these days. *The* market for Apple would be digital SLRs, but that would conflict with their "keep it simple, stupid" motto.