Everyone is talking about ROI. But that isn't why people are 'mining' , it is mainly for profit - with few exceptions of people who are just interested in the workings or want to support a coin (not applicable in GAWs case).
Why not just buy bitcoin and give it back to yourself after 4 months?
What is more interesting to see is how much you will continue to make after this ROI period. How much will you have lost due to inflation and time-value of money?
Do people think they will make much on top of the ROI? So much more that it is worth the risk or not even returning your investment?
Yes, that is why people mine. 1 if your mining a specific coin, you are supporting that network, 2 your betting that over the long term you will make more money by mining then by purchasing that coin straight up.
Eventually the difficulty curve we have seen on scrypt and 256 will level off. Scrypt is a different beast with asics because there are so many coins to absorb the hashrate. Scrypts earnings dropped faster than bitcoins ever has, but its leveling off faster as well.