My understanding is that the Rev. A thru D iMacs actually had more in common with the Lombard PowerBook, hence the use of laptop RAM and PowerBook-style CPU card.
Also, the beige's were OldWorld, and the iMac was NewWorld (again, like the Lombard, which was, not coincidentally, the first NewWorld PowerBook).
I could be wrong, though, so please take these observations with a grain of salt.
c