JimmyJoe and Greginator deserve to commentate simply based on their reputation that precedes them from 2014.
They have a way with words that really allow the audience and (especially) the stream to understand what's going on with the gameplay that's in front of them. Not only that, but the history and knowledge they have of the players allow them to provide background information and other important details of past events, player description based on character use and how they're able to compete with one another.
Also, no offense to BattleCow, but his commentary during the 2013 finals with Isai and Kikoushi was very biased toward Isai and quite obvious that he wanted him to win the tournament. You don't see that with these guys, they have a neutrality that allows the audience to be objective toward both players regardless of who is winning/losing.
Also, they bring serious hype. Just my two cents.