The differences in what you can expect to listen to correspond with the genre. You can pretty easily guess what you’ll be hearing in the next Elder Scrolls, Mass Effect orMadden. Sports and racing games seem to subsist entirely on licensed music, most of the songs being fairly popular singles released within the past decade. There is not much need for dramatic tension via music; most of this is provided by the competitive game play, while also tending to use quality sound effects and some sort of commentary. Any kind of formal score would seem very out of place anyway. Thus, the soundtrack for your Maddens or Need for Speeds serve as a sort of elevator music, keeping the silences at bay with recent modern-rock and hip-hop hits that get you pumped for that next game or race.

However, licensed music is not only used in this manner. In most narrative games, as in film, the music creates the setting and environment. This occurs through original scores as often and as effectively as it does as licensed soundtracks. Again, environment dictates this entirely. In Grand Theft Auto 4, licensed tracks create setting naturally, playing through standard, real-world devices such as car radios, stereos at your house, or the music in a store or mall. Previous installments of this series have effectively set the timeframe of a game in the 80s or 90s, simply by playing in the expected environment the songs you recognize as from that time period, without having to state that you are playing in the time. Bioshock or Fallout 3 accomplishes the same by using tracks with a distinct 1930s sounds.

Trends like this can increase the realism and the depth of virtual environments. It's true that the soundtracks of previous generations are more memorable, but perhaps that is because they were more catchy jingles, and not orchestral scores. The music did indicate tone, but in more of a pragmatic sense, and not in the subtle or emotional way it does today. 

We might not really remember the music that played at the end of Mass Effect note for note, but we certainly remember what we did and what we felt during the climax.