I'll disagree here. I'm sure the audio takes up a ton of space, as evidenced by past DLC size. Multiple channels, different vocals, and I'm not too sure about this, but, surround sound as well? I don't remember if the past games supported that, but that takes space too!
I'm just thinking back on SP. The DLC was like 2.5 MB an idol (32 MB or so for everyone), definitely compressed, and definitely with the dance as well. Can't remember anything about sound quality, though, and it was probably just stereo sound.
But I just looked at L4U's DLC. 800 MB a song? On plain stereo? What the crap? The dances can't take that much space, that can't be compressed sound we're listening to. I guess Im@s needs CD quality sound more than other games, but still... there were like 10 songs that came with the game (I think?), and I guess with the size of the DLC here, it's really obvious they filled the disc with as high quality as they could get away with. You want more songs and better graphics, we'll have to do something about this.
Like compress the source. You could probably bump it down to like 20 MB per idol (for the short, in-game version) and most people wouldn't be able to tell. That's me being generous too, even if it's just an estimate.