That's not entirely true.
When we finally reach the end of the rewards period for Bitcoin. It will not be cost effective to run bitcoin mining farms in the MW or TH/s / PH/s so you will see the difficulty lower astronomically and the return of hobby miners or maybe even just those who are doing it with whatever they have to be able to continue to allow for a strong bitcoin economy.
Not necessarily, if the bitcoin price will raise until reach something like that 10k dollars the mining will stay *competitive* but no one know what will really happen (because no one knows the future).
But I digress that time is far from now and I do not suggest using anything other than an ASIC to mine bitcoins and even that is going to prove troublesome if you have not ROI'd yet your ROI term is 100+days with new equipment and used alike.
Actually if you don't have free electricity the mining of bitcoin is *crazy*. The unique two problems are the cost of electricity (as I said) and the cost of the hardware machine itself.