There's a lot that's of interest in the Media Matters report which is embargoed for another 45 minutes, but Kevin Drum highlights one - the lack of anti-war Senators on the Sunday shows during the run-up to the Iraq war. Personally I think Drum's explanation - lazy bookers on autopilot - isn't all of the answer. Despite the fact that between 40-60% (or so) people were against the war depending on how the question was asked and at what time there were so few genuine anti-war voices in the media at all during that time. The lack of dissenting voices on the issue of the day speaks to something other than just lazy bookers, though I don't doubt that having Biden and McCain on speed dial had something to do with this particular statistic.
But, more generally, is there any reason for John McCain to have been on 124 times since 1997? Yes he ran for president in 2000, but aside from that he doesn't even currently hold an especially prominent committee chair.