Some time during WWDC, it was mentioned at a meeting that the new iPhone 4 has 512MB of RAM, twice what’s in the iPad or 3GS. This magical number isn’t mentioned on the “tech specs” page, or else somebody probably would have noticed it by now. Anyway, it’s just getting out that the 512 megs are there, and it explains a fair amount. iMovie being iPhone 4-exclusive, for instance — though I would have pegged that on the high-resolution UI as much as the RAM thing.
The extra RAM also helps with all the usual things, which we need not mention here. So — that’s one more feature to add to the next iPad version checklist. Higher resolution, front-facing camera, and now, more RAM. Sounds like a holiday update to me!