Sociologist David Reisman pointed out years ago in The Lonely Crowd that tastes in mass culture depend largely on social considerations; that we choose our preferences depending on what social group we'd like to belong to, what subcultural membership we wish to advertise. In this sense, every pop song is the same song, interchangable words in a social-signaling language.
This report provides more support for this view. Research published in Science suggests that popular music takes on momentum, becoming more popular regardless of quality. "Researchers found that popular songs were popular and unpopular songs were unpopular, regardless of their quality established by the other group [a control group]. They also found that as a particular songs' popularity increased, participants selected it more often." They speculate that this is a natural reaction to being overwhelmed with choices that are impossible to distinguish -- we look for cues of what others are doing and hope they're right. So maybe this explains the popularity of Dave Matthews?