Actually, come to think of it, there's a distinct irony in Apple products. They hate cables, so everything is as wireless as possible... yet they don't do wireless things very well. They selected a bad telecom to launch their phone; by the time they were able to get a good vendor, they screwed the antenna; the ipods never had radio - the one 'wireless' that's been around for a century; the Airports really suck as access points... :)

the rf stuff is pretty complex from what I understand. I think the iphone has around 7 antennas in it (wifi, edge, 3g, gsm, etc). I somehow doubt 'just adding' another antenna is a trivial matter, an expert would probably be able to tell you better what it takes to balance quality/interference with so many radios in close proximity. From what I know about how they work, I'm guessing they've tried out all kinds of stuff including putting in a radio, and probably decided to cut it.