I noticed it too that mfp seems to just throw a huge chunk of people on a 1200 calorie a day diet.
I just fiddled around with my mfp diet/fitness profile settings, and no matter which normal daily activities I pick it all kept my calories at 1200 if I want to lose 2 lbs a week. Only when I put it to someone with a very active lifestyle(bike messanger or carpenter), it raised my calories to 1320. No wonder why the forums there are full of posts of people being confused on why they haven't lost weight or gained weight when according to mfp they should have lost blah blah amount by then.
I think what MFP forgets to incorporate is that each person's body is different on how it takes in, burns and stores calories. Also the fact that not all calories are the same in how it effects the body. The more I look at it, the more low GL makes a lot more sense. It's crazy since at first I couldn't figure it out. But after reading most of the book and seeing how my body reacts to low or high GL, it just makes sense.