The problem is simple - The payouts are impossibly high with no variation like you get with real mining and there isn't enough left over to cover expenses. Moore's law doesn't matter, but there isn't even enough money to buy power, let alone replace the hardware.
I have this one theory whereby the people behind PBMining were in it at the beginning of the Bitcoin phenomenon and have got a HUGE stash of coins ALREADY !
Now what they're doing is to "advance the cause of BTC" by making it more attractive to more and more people ...
Perhaps they're subversives who despise the current Global Banking Industry and see Bitcoin as a viable long-term alternative ?