Originally Posted by JoshuaW
You definitely wouldnt be able to carb in cans, they would blow up.
This is definitely false. Surly, New Belgium, Sierra Nevada, and others all successfully can-condition their beers.
You are right that canning equipment is too expensive to be practical on a homebrew level. It's also somewhere between difficult and impossible to buy cans in a small enough scale for homebrewing. I've heard that some small commercial brewers even have to buy a year or more worth of cans because that's the smallest amount they can buy at a time.
EDIT: I've heard of one business (in Portland IIRC) that has a mobile canning system and they will can beer for homebrewers for some cost per can. Don't remember anymore details off the top of my head.