The idea is to try and gain new fans and do a better job of promoting the product: Gretzky lends the proceedings instant credibility and is a splashy get. Next step is for him to actually be good on TV.
Basketball players exist in a world where there are only nine other dudes on the floor at the same time while they are instantly identifiable since they wear no protective equipment. They seem to yearn for the spotlight while hockey stars routinely disappoint with how boring they are when given the chance to show some personality. Hopefully they include someone that has played recently and brings some personality to the table. Of course, anyone with personality on hockey broadcasts have also not been able to keep from getting themselves cancelled as of late so we'll see what happens.
Smith/Barkley/Shaq all immediately joined Turner following the end of their playing careers so, while they are old now, they weren't 60 years old when they started like Gretzky will be. Going to be interesting to see how he does. I don't want to see him just being diplomatic all the time.