Hello Cary,
The 3122 was chosen for a couple of reasons. The first being that it fits into a socket, and if something goes really wrong with the build, you can pluck it out and replace it with another one.
The other issue is that the 3116 (and so many others now) are surface mount parts. This gets us into the complication of getting a board printed, then stuffed with the chip. At that point, it begins to become trivial to pay the board house to stuff all the parts, and have them all surface mounted. If we did that, the price would go up, the fun would go down, and there wouldn't be a good way to tweak and service the PC board.
-PB
