Buying in april would also mean buying at the end of a large price spike. If you had purchased even a few weeks (or a month or two) earlier then you could have purchased a lot more (with BTC=20 you would have purchased 65 BTC = ~29k today, with BTC=13 you would have purchased 100 BTC = ~43k today).
Even though you paid in fiat for the machine you could have used that fiat to buy bitcoin
Good point. I didn't actually give Bitcoin serious thought until March 11, 2013 (the day of the chain fork on version .8, which happened minutes after I finished my all-day download of the core client!), so unfortunately those weren't options for me anyway, but you're right. At almost any point buying BTC would have been better than mining, except under CPU/GPU conditions. Again, didn't learn that until after my first experience with BFL, but I still made a profit, so I'm not upset at the lost opportunity because it's too late to do anything about it.
It is still, in theory profitable for people to mine, you just need to by the right equipment and have enough to invest.
The reason that CPU/GPU mining was so profitable is that CPUs and GPUs really never lost all their value in the same way that ASICs do. When an ASIC can no longer economically mine it will become essentially worthless while there are other uses for CPUs and GPUs therefore there is a market for them.