Maybe because cantis really kinda blow. I spend more time tweaking the damn cantis on my cross bike than any other adjustments on my three bikes. Setting the toe-in all the time to keep them quiet is such a pain. For thin road tires, calipers are great. The Tektro calipers on my SST AL are pretty damn good.
Once the tire gets larger though v-brakes or discs are better choices. I much prefer discs (Elixir CRs on my MTB, pretty amazing). If I could mount a rotor to my Aksiums for the cross bike I would definitely be running BB7s. I'll probably end up going to mini-Vs instead of replacing my pads when I wear these down mainly because I don't want to buy another wheelset (and 130mm spaced disc hubs are hard to find).