With the climbing difficulty there comes a point that the cost of a BLF unit will never be returned to a miner even at very high BTC rates.
The problem is most people don't know the first thing about economics. Look at it like this:
You have spent $1,000 for your ASIC. It is generating 1 BTC a month that right now is worth $10. In a year, you've earned $120. Now you are earning 0.5 BTC but the price of each BTC has gone up to $1,000. So now you are earning $500 a month. You've "recouped" your initial investment now in 14 months, right? Wrong!
Instead of spending $1,000 on that ASIC, you could have bought 100 BTC's at $10 each. Now, 14 months later, you have not broken even on your $1,000, but you instead have $100,000, 100 times your initial investment.
This is what people are failing to realize. They are considering how many BTC they get, vs. what they may be worth in the future, but the fact is that they would be earning a LOT more if they had spent their money to buy BTC outright and held it. Not to mention they would have their stuff right that second, instead of waiting it out.
People who paid, say 100 BTC back when they were $2 each for an ASIC are happy because they have made a few hundred in profit. If they had held those same 100 BTC, they would be worth $10,000+ now. In essence, they have lost money by getting ASICs.
This is only true in hind sight. Very easy to say now. Uncertainty and risk can move this the other way now. Although you are correct how many are applying this with alternates now. I believe all alternates are not being purchased with cash but most are with existing btc that have already gained in price.