Mining reward will only matter if you have low hashing power but if you have something over 400MH and cheap electricity the mining will still be profitable, this is why bigger farms are better, just two GPUs or three doesn't make sense unless mining is do damn profitable
Don't think this is always the case. Someone with 400MH still need to make a certain profit. 400MH gives like $25-$30 a day. Sure its almost $1000 a month however if mining dropped by half, it would be $500 a month. And its still a profit however you need to consider there are still some costs involved, not only the electricity. People don't want to be mining and barely breaking even.
Those with 2-3 gpus who are mining at home, they can mine at a slight profit or break-even, because they will most likely hold the coins and don't need to sell to pay their electrical and other mining related costs. Its still important that its relatively profitable for everyone, or else people will just close up their farm and liquidate their GPUs.