In a large number of sporting events, networks provide the following system: a person in the booth who is the commentator (I think that's the correct term, I'll use it for now) and 1 or more persons in the booth who are analysts. (Monday Night Football is the classic example of this.) When this system is in operartion, they each have specific roles to play.
(Forgive the use of the he, I know they can be women. I'm just being lazy.)
The commentator:
This is someone who knows television. He greets the viewer and is pretty much the anchor and host of the show. He imparts statistics, past results, overall trends and upcoming events. He's knowledgable about the sport, but you'll never (if done properly) hear an analysis. (Journalism vs. opinion.) One of his main jobs is to prompt the analysts, ask questions of them on behalf of the viewers, and lead the analysts by the hand through the broadcast if they are inexperienced.
The analyst:
Almost certainly a past player in the sport and therefore full of knowledge, able to impart to the viewer that knowledge to explain what is going on and to point out interesting aspects which the viewers wouldn't have known to look for on their own. He's full of opinions and assessments, but you'll never (if done properly) hear facts and figures about past wins. (Opinion vs. journalism.)
This is a very common -- perhaps the most common -- form of sportscasting. At the 2002 Winter Olympics, for NBC, Tom Hammond was the commentator, Scott Hamilton and Sandra Bezic were the analysts. Watch that team, or watch the ABC team, carefully, and you'll see that the commentator never does the analysts' job and vice versa. The commentator is always the first and the last person to speak to the viewer, saying "Hello and welcome!" and "Good-bye for now!"
Terry Gannon is a commentator, and I think he does a pretty good job. He frequently asks good questions and is good at prompting his analysts to elaborate or clarify something if he feels they're beginning to leave the viewer behind. He announces interesting stats and informs the viewer how well a skater has been performing lately, and about a skater's overall career. The analysts then play off that.
Everyone else who appears in front of a camera at ABC & Co. (except for the backstage interviewer) is an analyst.
I'm surprised at people who think Terry Gannon would make a good replacement for Dick Button. A good commentator does not necessarily make a good analyst and vice versa. He knows television and I have no doubt he's picked up a lot of knowledge, but for all we know, he still can't tell a lutz from a toe loop just by looking.
Personally, I think the ABC team works rather well.
However, Dick Button is beginning to stammer far too much and make too many mistakes on the air, and it is especially evident during live broadcasts. I know he's old and he sustained a head injury last year; this isn't a harsh criticism, just a fact. But he's such an icon and has such knowledge, I think ABC is in a bind; their execs must cringe when listening to him sometimes. I wouldn't be surprised if Dick Button retired from broadcasting -- voluntarily or not -- within the next two years. It's kind of like wincing when listening to sports icon Jim McKay stammer incoherently at the 2002 Winter Olympics, all the more painful for those of us who know how eloquent he's always been.
If Dick goes soon, will Peter Carruthers inherit his spot, or will ABC court a bigger name, such as luring Scott Hamilton away from NBC?
Perhaps, but it's all it the eye of the beholder I guess. 
