I don't know why he chose a 10" Paradigm sub, but it is my understanding that it had to do with price, his room area, and availability at local dealer. Most dealers here have their demo items, most models, and a very limited inventory, usually they'll order when you buy, and it takes about 2 wks to receive. Buying one from the mainland would have been more expensive, when taking in consideration that a subwoofer is a large, heavy, and bulky item to ship.
On the T55's he doesn't have too much room to play with them for properly, maybe a few inches, and that's it.