TNR's Michael Crowley:

I'm told that Biden appeared on every major network tonight except ABC (which only turned him down because Palin wasn't available, on an equal-time sort of basis).

If true, that's a grossly inappropriate decision by ABC. Particularly in light of the fact that the media has all but ignored Biden while paying a great deal of attention to Palin:

(The charts above come from PEJ's Campaign Coverage Index.)