say, for example, that you had the foresight to preorder a BFL single in July or August of 2012, they cost $1300 at the time...BTC were $13, when you finally got your unit, a year or more later, sure, you could mine back your $1300, but no way in hell it will ever mine 100BTC
I'd say that mining is a bit lower risk than buying, but lower potential reward. Unlike 2012 July, now the difficulty could be predicted a bit. So, I ordered a couple of Technobit HEX16B miners at about 1BTC each because the calculators showed that they would generate more than 1BTC (each). Maybe the won't. Maybe they will generate 0.8BTC, then I will lose some money. OTOH, if BTC price drops, difficulty could drop (or increase less fast), meaning I will generate more BTC. Difficulty could even stop increasing that much altogether (after all, it is easy to go from 1PH/s to 2PH/s, harder from 2PH/s to 4PH/s harder still from 4PH/s to 8PH/s and much harder from 8PH/s to 16PH/s - at some point the ASIC technology will reach the CPU/GPU technology level and will not be developed as fast as it is now).