Mmmm, good point about the heat. I have a friend in CA who is jealous of my mining, and he has a card that would do 100MH/s at least, but he won't mine because he said his room is already too hot.
Those of us who are adults can just go out and buy something to cool the room with, but some younger miners might not have that option available, and would just shut down the miners instead.
Adults like to lose money?
The only thing that determines profitability isnt how absolutely fast your rig is, but how fast your rig is compared to the total hash rate. Bitcoins increase in value relatively in step with difficulty of course, so you get more for more difficult coins. What matters is your chance of being the one to find it/being part of a pool that does.
The more people that drop off, the better it is for all miners, regardless of difficulty. In fact, mtgox might even show value vs other currencies increasing for BTC because its so hard to generate more - the money supply just slowed down, value goes up. And on top of that your chances just increased because people left - best time to mine, evar. But please dont, cuz Im mining right now. Let you know when Im done kthxbai.