for me it is the single reason for staying with cexio and that's the equipment being maintained by them, buying equipment is very expensive now and you don't see an ROI for a long time, by which time the difficulty is always increasing.
I dont understand on what basis do people buy GH/s on cex.io. 1 GH/s bought today at cex.io will make a total of ~0.01 BTC in its lifetime (assuming 30% difficulty jumps) and from mid may will actually start costing more in maintenance fee than it would mine.
For the same reason that people buy antminers etc etc is about the same amount per GHS