I'd love to hear the Karajan all-star Triple, either way. But it seems that Richter later came out against it, and some of the critics condemned it as being somehow a bad recording.
Probably it has to do with a certain amount of hubris that hit the industry at the height of the era where 'regular' people in the street knew big named musicians and composers. The idea that if you put them in the room, they'll talk, apparently isn't an invention of John Kerry. It's was popular in the 1970s in classical music, too. (Doesn't mean it's wrong, though.)
For an interesting discussion on that, see:
http://www.gramophone.co.uk/forum/recordings/beethoven-triple-concerto-karajan