I don't own an XM receiver, but my girlfriend does, so I listen to it on long car trips, and occasionally on my Treo.

I enjoy the three stations you mentioned (Ethel, Lucy, and 90s) but you have to understand that they're all focused on basically the same musical neighborhood, so, if you're listing to mostly those three stations, you're going to get some repeats. Ethel and Lucy in particular have a lot of overlap, though Ethel plays less of the late 80s stuff and Lucy plays less modern rock. And the 90s channel just plays popular songs from the 90s, and, surprise! a lot of that was modern/alternative rock.

I like all three bands you mentioned, and I think U2 and RHCP do come up a lot, but did it occur to you that those bands just had a lot of hits during the time period covered by those stations? (I've never really noticed a lot of Social Distortion, and wouldn't mind more, actually.) If there's any significant deviation between how much airplay those bands got in the 90s on terrestrial radio and how much they get now on XM, I'm not hearing it.

But, apparently, some others are. Here's a blog post that mentions "the U2 issue." Someone on the Internet agrees with you, so you must be onto something!

Anyway, it just so happens that a few months back I wrote some Python code to scrape XM radio's site to collect what songs are currently playing. I never did anything with it, but maybe for fun I'll collect data for a week or so on what songs are played on those stations, and see if you're onto something, or just on something.