From a roleplay/world building perspective, I really like the fact that Fallout New Vegas has an extremely limited radio and I do think the atmosphere would be seriously damaged if they had added more songs. I haven't played the other Fallout games but I reckon this is probably applicable there too. I understand that people get bored of the same songs over and over again, but that's a feature not a bug. If you were living a hard scrabble life a post-apocalyptic wasteland where no one has the means or resources to be writing, recording and distributing popular songs, yeah you'd probably get bored of listening to the same music over and over again. And then when you turn the radio off, all you can hear is the creepy horror sounds of the Mojave and suddenly listening to Jingle Jangle on repeat doesn't seem so bad after all. The repetitive, upbeat soundtrack is super effective at making you feel like you're stuck between two not so great choices, one awful and one somewhat better but severely lacking. And that really reflects what it's like to live in the Mojave--you often don't have the luxury of a completely satisfying choice because you and everyone else is fighting for survival. Specific to FoNV, it really drives home the political climate of the harsh, brutal Legion versus the comforting but stale and ineffective NCR. Honestly FoNV is the first game that really made me think in depth about the music choices in a video game and I'm really really glad they made this choice.

I am pretty sure though that the Big Mountain DLC added a new radio station.