I think a lot of brand loyalty boils down to a console you first owned. I got a NES for Christmas in 1990, which could have easily been a Master System. I was only 6 at the time but Mario and co stuck with me. So then the SNES became a logical choice, as opposed to the Mega Drive. Also, as a child, you're limited by what your parents can afford - so of course the next was an N64.
By the time the Dreamcast and Gamecube were available, I had a bit of financial freedom so I had both.
As an adult, but with a limited amount of money, I have to make choices so loyalty plays less of a role. I bought a PS3 when the slim was released as my brother had a PS3 so it made most sense to play, for free, with him. Bluray was a big bonus. I will by no means buy a PS4 over the next Xbox if it's not as good. I may not buy either.
I am unashamedly unable to not buy a Nintendo console, despite a dearth of games for the Wii U at present. Even the wife knows this, so she bought my Wii U for Christmas this year. I suppose I value playing the next instalment of the games I enjoyed so much growing up outweighs the console's popularity.