Hmmm... looking at the source available it looks like Google and Amazon look ups were disabled for some reason, it's possible the other look ups are also out of date stopping them from working like that. I guess I'll take a look at it in future to see if I can fix it up unless someone checks it out first.
I think I posted a reply to the same question in our other thread about skins. However, I have contacted people at the MusicBee forum and asked where MB gets it's streaming art. One of the regulars said he was stumped on that one, but that the stations send out the cover art, which could be where MB finds them.
"I would assume it depends on the stream. Quite often the streamer sends art along with the track/artist information. When it doesn't, I don't think MB goes out and gets it. I may be wrong about this last part, but that's my understanding." --phred from Music Bee (very knowledgeable member)
I've also noticed that "some" skins for AMIP also have streaming album art or "covers."