I don't really get why someone would invest so much in mining just to have to wait a really long time to just get your money back (hopefully)
Well now is not a good time to sell BTC... so while waiting, he takes a chance of perhaps diff increase slowing down. if he makes 30% in that instance, so much the better... if he just makes or loses 5% (as is more likely), well, no biggie... thats my guess as to how he sees it.
Plus or minus 5% on that kind of investment doesn't seem worth the risk! Good luck to him or her!