I like lists! :D
1) So let's say you're right and there is a pair in the $300 range out there that I would think sounds better (remember, it IS largely objective). First of all, that still doesn't mean it's overpriced or even overrated. Just that it might not be THE BEST OF THEM ALL. In my opinion, if it's this freaking difficult to find a better pair of headphones, there should be no hesitation for ANYONE to suggest it at its price point.
2) Sorry, not gonna do that. Under no circumstances am I going to drop money on a headphone I don't like and then fight with Craigslist and the Head-Fi classifieds for months on end trying to pawn off what I bought so I can try another. If I don't like a headphone after an hour, I'm not interested in listening to it for multiple hours, let alone weeks. That tells me that the benefit of this headphone is pretty minuscule.
3) Furthermore, there ARE the other factors. Okay so we have the M100 and Headphone X that are of comparable sound. The M100 is built like a tank, looks great, has an amazing warranty, AND you can customize it. Even if the sonics alone are only worth $250 (which isn't correct at all), the rest you get easily makes up the difference. But again, I'm serious, suggest some to me. Because I, as well as countless reviewers like Tyll, seem to think the M100s are the bee's knees.