The extremely fat version (12 discs) is indeed the boxed set of every disc that's in the Extended Versions. You'll get them cheaper than buying them all seperately and you get them in one box instead of 3.
I've ordered a good bit of DVD's and CDs from Play.com and they're fantastic. If they're in stock they arrive within a day or two, a lot cheaper than most other places and I've never had a problem.
