For the same reasons that Sennheiser produced the HE90, and Sony produced the R10. Company pride, and company prestige. IMHO, these are important qualities for outstanding companies, as well as for outstanding teams. BTW, there was a hint that John is considering the development of a combo-dynamic/electrostatic headphone. I hope that he listens closely to an HE90, during the time that his company proceeds with such an exciting development, if they do.
Although I do agree with you partly, I do not consider it a necessity. Sennheiser & sony are big players. Just because Microsoft does something fancy (and they can totally afford to loose all the money they put into it), it doesn't require Apple, Linux, etc. do something for just the sake of excelling it and by not doing so, it doesn't mean that they have failed. As an average Joe, i really don't care if Grado makes a $3000 ultimate headphone, 'coz I won't be able to buy it. i would rather that they spend that time meaningfully in improving/inventing products for the larger purpose. Its just my views..