The Philips X2 headphones should not be getting the 3rd most votes for the fact that they are not below $200. If someone has a link showing me otherwise then I will buy them immediately!
It's probably because they look better, sound a bit better, and the build quality is a bit better. It's the same reason people still buy iPhones even though they are essentially the same from the last year. The higher price inflates our notions of quality, it's all psychology. I personally voted for the HD598 so I'm a hypocrite. :P
The reason people feel the need to buy iPhones every year is because either they've physically damaged the device and don't realise that repairs can be had for MUCH less than the $279-swapping fee Apple imposes and/or their device (whether they're consciously aware or not) has slowed down due to the technological restraints (such as low ram or disk space vs what is commercially available at time of release) and/or via software "bloat" whereby code runs much more inefficiently on older devices, which has been widely recognized right after every new major iOS release.