That's the theory. In practice, people who think that $15 are too much, will either forget about it (and not come back when its cheaper), or they will pirate it.
(1) As for forgetting, well, good companies often market their price reductions. I mean, famously, Apple released two iPhones in 2007, a 4GB one at $500 and an 8GB one at $600, and rapidly killed the first and reduced the second to $400, after about two months. It made a terrific marketing splash, lots of people bought the $400 one. Granted, this sort of marketing is easy for them because they're Apple and everybody is always listening for news on them, but my point is just that "we're reducing our price!" can be a subject worthy of a new press release and a new Hacker News bump.
You may also remember that so many people criticized them for the above, that Apple gave away $100 certificates to the people who bought at the $600 price point. There is a valid criticism of what I have said above which nobody has yet mentioned: which is that people like to get a "good deal" and think of you better as a company if you provide that to them. As you try to extract out ∫ D(p) dp from people, you are also squeezing a commensurate amount of happiness out of them, and that can be bad for long-term customers.
(2) The top isoHunt torrent lists 20-ish torrenters, so I'm not sure whether piracy is a valid concern on this matter.
