Yep, personal preferences, and performance that is often closer than we care to admit, and a general expectation bias and sensitivity to slight SPL changes and frequency balance changes, etc... Many folks around here want clear winners and losers, but it doesn't work that way. One of the reasons I enjoyed Brooko's write up so much, and that includes his own conclusions, is that I could see it turning out that way even though I leaned a slightly different direction.
After my first few days with the HD600, I posted in another thread that I felt kind of dumb for not starting there first... I saved for the HD700 because I was afraid I would be disappointed with the 600 or 650, but that is clearly not the case. With the right amp and music, I could easily spend more time on the 600 vs the 700. And there is a coherence/balance/organic quality with the 600 that is much harder to connect with through the 700. I was even nervous that I would find the 600 to be bass light and wished I had gone with the 650 instead, but I wanted as much clarity and neutrality as possible for that particular purchase so I joined the HD600 cult and boy am I glad I did.
I am trending towards "newest is king" in my collection also as of late, but not always, and in my defense I have to say that each experience and continued research gets me closer to making choices that fall more inline with my personal preferences. I have a pair of ATH-M50xBL on the way however, purchased because I just wanted to have them in my collection and something nice for guests/tracking in the home studio. If I think they sound better than everything else after a few days, I am in real trouble.