I think comparing Johnny and Rod to Rich is a bit complicated. While I thought Rich was a decent announcer when he was first hired, it seems like he has greatly changed over the last year or so. (Just watch his older shows on YouTube). Johnny and Rod however, always sounded the same -- they were professional voice artists, while Rich was a weatherman.
To me whenever Rod and Johnny were on TV, they had their own persona about them. Rich comes across now as just looking like someone who is kissing up to Drew. I never felt that way with Johnny or Rod in relation to Bob.
I don't quite know what it is about Rich's demeanor to make me feel that way, but perhaps it's just the over the top "announcing" or some of the ridiculous things that he subjects himself to on the show, in "Drew's style humor."
Rich has gone from a somewhat classy announcer to a mock Andy Richter. It's almost like since he wasn't involved as much with Bob, he's doing whatever Drew says just to get recognition and face time, even if it means blowing his career in the hopes of being Drew's sidekick for life.