It's inevitable, but you're right to wonder if it will impact consumers at some point.
I can foresee Amazon driving out the competition and eventually jacking up prices because there is no competition. Or perhaps that won't happen because of other online retailers.
Either way, local retailers are mostly screwed...
Thats what ultimately scares me about one company having a monopoly, but if they did that eventually more businesses would enter again. I think they would rather have their hand in everything and keep the power.