In any other field, I'd probably agree with Bonnie Bernstein, but not here.
The typical fan doesn't care who the announcer is, just that he/she does a good job.
The diehard football fan prefers someone who has played football, and that at the highest level - someone with name recognition and who has an engaging personality.
Usually, players have to have rings to get these positions. But Tony Romo is just a tremendously likable person, is/was the quarterback of the most recognized football franchise in the world and has an intimate knowledge of the game. Plus, almost everyone who pays attention to football knows who he is.
As long as he doesn't talk like he has gravel in his mouth like Shannon Sharpe (whom I actually like), Romo should do fine.
As an aside, I was listening to my local sports radio talk show prior to Romo's retirement. I listen to any football news they might have. When they get to the football segment, the announcer says, "No update on Tony Romo's situation so we can skip football news." THAT'S how popular Romo and the Cowboys are.
And that's what CBS sees.