IMO it comes down to individuals plus perspective.

I don't mind saying "I am Bipolar", this does not reduce me to my disorder, nor do i over identify with my disorder. Its just basically 1, out of habit, and 2 it feels more a part of me than some germ or disease I caught or picked up somewhere.

Point is i am comfortable identifying this way, and i don't need anyone to feel sorry for me for doing so.

I also have nothing against the opposite side of the camp who say "I have bipolar disorder", they obviously find that works for them.