You're definitely on to something. I'm of the belief (as are many here that I've seen) that they should wait until like...week 6 or so to start ranking teams.
I would have to say, though, the whole process would become even more convoluted if there were no polls until the end of the year. There has to be a way to write some huge algorithm that can help us calculate which teams are the best and which aren't, taking everything into consideration. But until then, I believe that ranking teams "makes it easier" to decide playoffs, bowl games, etc.