I don't think the Blues are necessarily politicians, they are idealists and activists, and it is an indicator of the current state of the Tower that idealism and activism translates into political scheming and power games. The political focus is hardly unique to that Ajah, either. How many Yellows do we see running around the world looking to Heal? All of them seem far more oriented toward the Tower than might be expected, and only the Reds have the excuse of being on top of things, what with the world remaining unbroken for three thousand years, and even RJ giving them credit for being so effective at hunting men that they have culled the trait from the population. Every other Ajah's chosen specialization seems to have a negligible effect on the world, except maybe the Whites, who explicitly don't care. What matters in choice of Ajah is how and why you use whatever skills, regardless of with which Ajah they are generally associated.