I think Terry has a point. Another one is that a 737 (as old as it is) has somewhat more sophisticated systems than a C172. Since it's commercial with the 737s, I can understand that they don't like alien gadgets, that are similar to the onboard systems, used onboard. I also understand the argument that a GPS like this makes no more interference than a laptop but perhaps we're better off safe than sorry.
We've all forgoten to turn of our own cell phones more than one time so perhaps it's not that big a deal.