Difficulty increases are across the board, whether the new miner with one 4650, or the super miner with 20 rigs of 4x 6990s. Everyone will be affected the same.
No it doesn't. Assuming conservative price rises in the future per BTC, there is a difference between your earnings dropping from $20 per month to $1 per month, or from $19,500 to $975 per month.
For the guy with a 4650, he is just wasting his time in September. The guy with 20x 6990 is still earning way above the cost of electricity so it pays off to keep going for at least a month or two, maybe more.
because supply never gets any lower, it is always there X amount of bitcoins on the net.. it is NOT a consumable
Have you ever heard of transaction fees?
There is only a limited amount of bitcoins that will ever exist (21m) yet transaction fees slowly eat them up as well. Which means there will be less and less of it to pass around as the years roll.