i think in the first place they were not going to give certain classes any gear from certain GC's, so that all the GC's had a sense of individuality. but then they thought this might make one GC more popular, so they decided to allow any class get gear from any GC. but at the same time they had to think of a way to keep GC's individual and that is why the gear is slightly different.

(its this sense of being different that installs loyalty and pride in your GC)

go maelstrom