A good observation. Still, it's not too different from the big three that existed a couple of years ago: Sennheiser HD600, Beyerdynamic DT880, AKG K701. Sennheiser has actually re-cycled the design several times: HD580, HD600, HD650. Beyerdynamic offers several flavors of the DT880: Pro, Premium and I don't know what exactly - but then there's the "Manufaktur" edition, too. I think the biggest difference is that perhaps: Beyerdynamic does not market as much as AKG, while both Beyerdynamic and Sennheiser continue to push the barrier with the HD800, HD700, T-1, T-5p, etc. Until AKG came out with the K812, it seemed that all AKG was interested in was marketing and no other "new" headphone designs.
In any event, the now mid-ranged headphones mentioned above were/are world-class headphones, and perhaps better bang-for-buck headphones than any of the flagship headphones currently offered. AKG may have gone about things a bit differently than the other two, but it doesn't detract from the validity of the design. JMHO.
There are complaints about my favorite headphones as well - Grados. Same driver, same design for almost every headphone. They simply re-package it with different ear cushions and different cup materials/shapes. Then again, what else does headphone design involve if the driver is optimized - other than comfort and aesthetics?
I remember, with the recent Sennheiser interview with Co-CEO, he said something like there's no point of making a new headphone in a better design with the same old driver as used before, Sennheiser wanted new driver, new technology and improved sound for every of their new headphones combining with new stylish design.
^ I pretty much agree with that. The Grado IMO already have decent design, no need of changing. But then again, I am part of Grado Fanboy so yeah xP