Couldn't you turn it around and say it's unethical for Apple to allow customers to buy phones knowing full-well that they are going to introduce a top-of-the-line model in a few months?
W...T...F?!? Please, please explain this logic to me. Honestly, I don't understand how some people think like this! What would you have Apple do? Stop selling the previous model as soon as they have the first prototypes of the next one? Pre-announce the next generation of phone at the launch of each new generation?
Are you familiar with the Osborne effect? Is it really so bad that Apple has managed to, more or less, completely eliminate the Osborne effect through their over-the-top secrecy? Why should you be entitled to know what some other company's plans are?