IEMs are NOT a niche market; and gradually even the more expensive ones ($200+) are becoming more and more 'popular' - a completely different situation from that seen only a few years ago. You can clearly see this by the ever growing IEM market with lots and LOTS of new models coming out every few months, quite a few of them being well over $100, something unthinkable only 3 years ago.
Also, I very much disagree that "most IEM buyers use headphones at home". Perhaps a lot of head-fiers do, though not necessarily most, and certainly NOT most people out there (outside of Head-fi).
I also strongly disagree that "the engineering constraints justify the high $". I said earlier that perhaps $200 would be a more realistic/ fair price for these top-tier IEMs - and that, honestly, would still be quite a bit of money.