That commercial break thing started with WCW. Used to annoy the hell out of me, but I don't watch much wrestling anymore so I don't give a damn.
I can remember back in the day (before the WWE Attitude era) when commercial breaks were done before or after a match. . . usually they took breaks after a locker room interview by Gene Okerlund. Ahhh. . . memories.

EDIT: Now that I've had time to think about it. . . I actually first saw mid-match commercial breaks on Saturday Night's Main Event. Considering it was supposed to be a live show, they took commercial breaks during the matches.
The only times previous to that I remember it being done was during 60 minute time limit matches that were aired on TNT (Tuesday Night Titans). They'd take breaks when there was a lull in the action.