Below is the pattern for Democrats. The distribution is pretty flat, meaning that liberals and moderates are equally likely to appear on the show. Only the most conservative two deciles stand out as unlikely to appear.
Now check out the distribution for Republicans. More moderate Republicans are highly unlikely to appear on the show, but the more conservative half of the caucus is much more likely to appear.
I still don't have a great sense of just how members of Congress get booked on shows like "Hardball" -- whether it's due to the own initiative, whether the shows actively seek them out, or what. Harris suggests that the parties themselves are increasingly acting as booking agents. If that's the case, they're clearly approaching the job differently.
It would be interesting to see whether this pattern holds for other political programs.