What they are doing with a single guitar performance is concentrating on the "meat" of the song. Which can be done quite easily once you know the song structure.

While it's not a site like GT or TF, Karaoke Version is a tremendous site that allows a user to download custom backing tracks for virtually every song you could think of. I've not been disappointed yet. So, you can pick drums, bass and vocals as an example - you supply the guitar. With Karaoke V you can use any teaching site or YouTube video, get the meat of the song down and have your own backing track to play to.