But, if I purchase the miner instead and the price drops to $70, I always retain the option to sell the miner. For example, selling the miner purchased originally at $1500 for $1000 at a $70 conversion rate, I can receive 14.28 btc for it, and that's on top of the few btc I would've mined already.
Yes you do have the option to sell and earn like you have described.
Notice that if you do sell if for 1000$ or 14.28BTC, together with the BTC minded before selling, you could end up with more than 15BTC!
15BTC which were impossible to mine directly with that miner! (according to your scenario)
but the only question is, who will buy it for 1000$ in this situation? (assuming no stupid people in the world)
Why buy a miner for 14.28 BTC with no chance to mine 14.28 BTC with it? ( "No chance" becuase this is the situation you have described).
It's is better to just buy 14.28 BTC directly rather than buying your miner!
However, the value of an ASIC is not "purely" determined by the BTC it generates because the value of an ASIC in terms if btc is mediated by fiat conversion rates. If I spend $1000 on an ASIC that makes 0.1 btc per month, it's a good decision if the value of btc is $10,000. It's better to receive 0.1 btc valued at $1000 than to receive 1 btc valued at $100.
Here, again you assume that one will sell you a miner for 1000$ which will make you 10000$ a month (0.1BTC).
Who is stupid enough to do that?
You can play all day long with hypothetical scenarios which requires a stupid buyer/seller but in the end it all comes down to this :
To buy and to mine are both equal to acquiring BTC.
The better way from these 2 options is the one which ends with more BTC in your wallet than the other.
And in that same "better way" you would also have more USD comparing to the other way (becuase more btc is more USD).
The hypothetical examples you selected are much more fabricated than the hypothetical example I gave of the BFL Single which suggests a realistic scenario unfolding from present market data. I created the examples you selected as extreme cases that simply highlight the plausibility of the scenario -- if extreme examples are plausible, non-extreme ones are indicatively so.
Addressing the part I have bolded, keep in mind the name of the game is ROI independent of whether you initially purchased with, or whether you end up with, fiat or BTC. Every miner I have purchased (with the exception of the BFL pre-order which will never achieve ROI) I purchased with fiat which has allowed me to achieve ROI, even with block erupters.
If I had purchased BTC at the time I purchased erupters, of course that would've been the best scenario -- hindsight is 20/20, and we all know the price of BTC has steadily increased throughout the past two months. But, purchasing erupters with cash has allowed me an opportunity to achieve ROI and then some, and I will still achieve ROI even if BTC drops below the price it was at the time I purchased the erupters (i.e. assuming the price doesn't REALLY drop, like to sub-$50). I purchased the erupters knowing that BTC ROI would likely never be reached, but yet I still bought them anyway. Now, why do you think I would do that? It's because I knew I could make money with them even if BTC takes a dive because there are tons, and I mean fucking TONS of irrational, stupid buyers. Quoting Tommy Boy, I could sell a ketchup popsicle to a woman in white gloves in this market.
Why didn't I buy BTC instead? Because there is no opportunity to profit in that scenario if the price of BTC drops. With a miner, I can make money whether the market moves up or down. Buying BTC outright, I can only profit if BTC goes up.
And, I disagree with your way of selecting a "better method" which you have defined as whatever method allows you to end up with more BTC. By purchasing a miner, you simply have more KNOWLEDGE to guide your financial decisions, and not only do you know where you stand in the present, but you can predict on an ongoing basis where you will be in the future. To me, this can be a much "better method," not because it yields a larger profit, but because you can calculate your actions instead of essentially flipping a coin on the market and hoping for the best. And, with the bullshit clients are frequently experiencing with various exchanges, I'd argue that it's just about as easy to get someone to buy an ASIC for an inflated price as it is to exchange BTC for cash in your pocket.