It's because (d) NO "KILLER SONGS" EVER PLAY ON THE RADIO. Unless you're lucky enough to live in a college town, "the radio" is a horrible thing.

I find out about new music from friends, or reading the occasional music magazine, or chasing links on review sites like Pitchfork... in general, by keeping an ear to the ground and actively seeking out new music.

I've been enjoying emusic.com too, as a way to chase "related" bands (labelmates of bands I like, generally). Haven't turned up any real gems yet but I have hope.