Once you get used to hearing a good bass line, songs without any bass, or even synth bass, just don't sound as good. Granted, it takes some good hearing and concentration to gain the full benefits of a bass line, but in the end, once you've heard the masterful bass playing by musicians such as Chris Squire and Roger Waters, a bass' presence will never be fully replaced by synths, and no bass at all, as Peter20 said, makes for a really dry, empty sound.

Maybe it depends on which genre you're listening to. Punk and hard rock, for example, often drown out the bass, and it's presence adds little if you can't hear it. And in some other genres, the bass is actually brought up far too loud, such as in some rap or techno songs. But in a regular classic rock track like I listen to, it can make all the rhythmic difference between a good and bad song.