I'm not an expert on all these companies but what you say is partially plain wrong - one just don't hear about it the efforts of Sennheiser. Don't get me wrong some of them have very good singles labs or something but there is a lot more to it. Sennheiser have more people just in research of headphone only related topics than most competitors have people involved in the entire headphone related chain. In fact I often to tell people when explaining about Sennheiser Communications and why their products are qualitative better than say Bose that they have more highly skilled people just at researching labs from Sennheiser and William Demant combined in researching into audiology topics than most other companys have staff in total related to audio including marketing, logistics etc. William Demant even spend a lot of money on research that isn't totally for gain of competitive advantage but for everyones healthcare, like advancements in training of audiologist, as they are own by a foundation for promotion of better hearing etc. And Sennheiser is known for its very strong global marketing and sales division despite some conservativeness - again due to importance B2B divisions.
What you can ague is the outcome but to say that anyone has near the research or resources that Sennheiser has is just silly. If some of the others had access to say mass production capabilities of their own speaker designs like Sennheiser does they would have been able to lower their prices on anything but the top models. HD202, 555 or MM50 for iPhone is good examples that competitors can't keep up with the overall performance for the low price segments so these sell like hot bread. On of the reasons Sennheiser still has a headphone division - the profit isn't in HD800 or that sort compared to R'n'D costs. Its something the Sennheiser family choose to let happen - just like the PC350 gaming headset I'm told was a long and hard struggle too as it wasn't expected to profitable (clearly before they really realized how much we wanted something better than the other poor headsets out there).
And it isn't going to end here - I've seen what coming out next year or the year after that and some of these products are defiantly made of the love for quality experiences at higher than most consumers would buy price points - the marketing guys just hope they will be the new HD800 or PC350 and at least regain some of their investments.