They also say they are tricky to set up, and don't stop as well. Of course, working in the auto biz, I saw that when fuel injection replaced carbs... Now I wouldn't wish working on a carburetor on anyone. I digress.
If there is a tricky system on a bike to parse out, I pick you to make it work. But brakes are an important part of a bike, and being able to slow down, or stop on request, should be at the top of any list. Again, using it for other than cx may sway folks towards disc, but I can't say for sure if that's the hot ticket for cross yet.