Finally, to address the notion that "if the cap was per job, I would be forced to play a specific job in order to gear said job". Well… ^^; … you're entitled to your own tastes, but doesn't that seem more logical to you? That you need to use a specific "asset" (here, a specific job) in order to be more powerful/efficient with the asset in question? How is it logical that your tanking gets better when all you do is use a healer?
Think of it this way: I don't get better at maths when I read history books, I get better at maths when I actually learn and do maths.
Of course it's nice, it's comfortable to be able to gear all jobs only playing one, but it's certainly less logical than having to use a given "thing" to get better at that very "thing". It would be great to get better at maths when reading history books as well, but it just doesn't work that way. And let's not even talk about "player skill" when you gear up a tank by playing another role entirely. It's just how MMO's work: I play a tank, my tanking character gets "better" (geared), and I as a player get "better" (skilled) at tanking. I play a healer, my… oh you get it.