Nielsen: More Teens Now Listen To Music Through YouTube Than Any Other Source
techcrunch.com
techcrunch.com
Youtube doesn't use MP3s, but AAC for hd content, which provides even better quality. There are numerous tests that compare AAC at 64kbps to MP3 at 128kbps.
Often artists upload music attached to HD still picture, to ensure that high quality encoding is available.
The low quality is not an issue with Youtube audio bitrates, but problem stemming from people uploading low quality sources. Audio re-encoded multiple times. It is common to find a mono music with 12khz cutoff.