When buying speakers I'd try to focus on decent brands and proper reviews that test them against other speakers rather than just relying on reviews from people on sites like Amazon. The wattage rating does roughly relate to how loud it would be but I'd never focus on it, you can get high wattage speakers that sound terrible. How good a piece of audio hardware is really can't be judged from the specs alone, you really need to either hear it for yourself or failing that, find a test done by an audio expert.
Manufacturers of cheaper speakers tend to also have a tendency to state ridiculous wattage numbers that the speakers have no chance of reaching. If you are looking at wattage, you should be looking at the "RMS" wattage and ignore anything that says things like "Peak" or "PMPO".
