The old rating system granted up to five stars but now the maximum number of stars is ten. This signals that they wish to start exaggerating the quality of the product. When there are only five stars you know that they are laying their reputation on the line when they grant five stars to a new CD. (Michelin of course won't give a restaurant more than three stars. They don't calculate out to the fourth decimal place along a scale of one thousand.) If the music isn't good you can decide to stop trusting them. But say they give a new release eight, nine, or who knows maybe eight and a half stars? What exactly are they trying to say? Yes they are putting their reputation on the line when they give ten stars, but this will happen so infrequently that it will be harder to judge their overall trustworthiness.
Evaluation systems with fewer and grosser distinctions are often more credible because they are easier to monitor.