i'm going to put the question off, because it seems like they're actually a three piece, and while it's not bad for what it is, it's actually pretty good for what it is, it's not what was going to drag me out in the cold - i was expecting at least some kind of extra arrangement.

i don't know if those extra arrangements were done by somebody else in the studio or what, but every video i can find has them performing as a three piece.