I think safetyblitz has hit it right. The "colour" guy tries to provide some insight into the game that will appeal to fans of all levels. My wife will watch with me (usually while reading) and she does find some of the comments interesting. Me, I don't care about what the QBs dad taught him in high school or that the receiver's best friend was a down and outer.
I find Gord Miller can be a little irritating when he does his bizzaro stats thing. Like, 'this is the first time that a team with a running back with four letters in his first name has run for more than 53 yards in Commonwealth Stadium since 1996' kind of thing. Drives me crazy at the World Juniors Hockey tourney, and tends to drive me a bit nuts here as well.
Having said that, I think his work as a play by play guy is super. I liked the banter he and Pierre McQuire had, and I like his short backgrounders on players. A few lines once in the game and sort of in the "by the way" fashion. Not trying to impress us with his knowledge, just kind of sharing it for interest. I'd like to see him do more and Chris Cutherbert less. And the next guy to call Cuthbert "CC" should be forced tor run wind-sprints during half time.
All in all, I guess it is a tough job to talk for almost 3 hours and be interesting to everyone, all the time. I have a brother-in-law who does the talking thing exceptionally well during games, but misses the interesting part by a looooong way! So I speak from personal experience.