Well, price, for one. More capability can push up the pricetag.
But Apple also likes to push new approaches. They were the first to eliminate the floppy drive, now they're eliminating the USB port on the tablet....maybe that backfires, maybe it pushes things in a new direction again. Time will tell.
With the iPad, saving an internet file-storage service there's no way to get a personal file from your PC to the iPad (that I am aware of.)
I'm not terribly familiar with the specs of these things, but couldn't you just remotely log into your computer over a wireless LAN and copy whatever that way?
Yeah, I suppose you could. Still seems to me that a USB port would be useful in some situations where maybe a LAN wouldn't be feasable. It just seems like an oversight that shouldn't have occured. Removable/movable physical storage just seems like one of those things that should've been on the iPad from the begining.