I'm a cold natured person. It's possible that you've spotted me in the parks, I'm that odd person wearing jeans and a cardigan in 80 something degree weather. I, generally, keep my AC at 74-76 depending on the day's humidity. My mother on the other hand likes it to be 72 or lower, so when we go on vacation I try to let her control the thermostat and just wear layers.
So, when we stayed at AKL this summer we had it set at 72 at first and I was HOT! We had to knock it down to at least 70 maybe lower. We may have been stopped from making it cooler than 68, can't remember. I can't imagine that the thermostat was right about it being 72. And, it's not like I'm just not used to the humidity or something, I've been going to Florida since I was 4 and Virginia can get pretty humid too.
So, if you get a room with a thermometer that's off by a few degrees on the thermostat, having a 68 minimum would be a problem. The thermostat where I live is off by about 4 degrees, but it's not a big deal because I just take that into account when I set it (mine says it's hotter than it is).
I can understand Disney wanting to set a minimum. I think 68 is too high, but even if they made it 60, there are still going to be some people that think that's too high. I honestly don't know what the compromise figure should be. I've never had a problem with the motion sensor. Maybe we just move in our sleep a lot.
OP: Did you ever stop by the front desk?