Figured this theory is more appropriate in this thead even if it doesn't contain any spoilers:
Well, the books are called "A Song of Fire and Ice". Clearly, fire and ice are two oppossing forces in the world of GoT. Ice seems to take the form of the white walkers, whereas Fire intervenes through its followers. Presumably, we only see the influence of Fire through its believers, as it unlike Ice cannot be embodied (though it can create killing shadow beings, just as fire creates potentially poisonous smoke) - it is a fleeting force of nature not unlike that of the fire burning in the hearts of men (e.g. passion).
Ice on the other hand is fundamentally embodied in the world, as, well, ice. Therefore, instead of religious folk carrying out the will of Winter (I guess some people count as believers though, like that dude who fucked his daughters), Ice simply has chosen to embody itself in physical ice avatars.
Perhaps this is at the cost of being able to channel magic into ordinary beings, it has to channel its magic through its embodied form, like when white walkers resurrect dead people into zombies. That's a significantly worse version of the resurrection Lord of Light followers have access too, perhaps because the LoL can in addition to its own power draw upon the innate life force (or internal fire, passion) of its subjects as they cast the spell - which is why we get drastically improved resurrections. Or maybe ice is just antithetical to life, as it is usually not depicted as a crucial part of humanity (unlike fire, which has plenty of analogies in the nature of men)
I dunno how dragons play into this, as they seem to be embodiments of fire - avatars of the fire god. It seems like that would throw the balance in favour of the fire god, which is maybe why winter is coming - to kill as many men as possible so as to reduce the power the god of fire can possibly draw upon, and before the dragons grow up to become a threat.
...
That does seem to be the case, yeah?