I don't like their explanation. This tells me that The Shield is going to win but they don't want to put it in the Chamber because it might hurt Ryback, Cena, and Sheamus's momentum. To me, losing in a regular tag match is worse than losing in the Chamber. Give the fans a great match inside the Chamber and they won't even care who supposedly looks weaker.
The dirt sheets explanation is that if this match were an elimination match, likely only one guy would survive. Meaning only one guy would get the post match celebration and credit of winning. And the other five would look somewhat weaker. This way, which ever team wins, you have 3 gus who get the post match celebration and two guys on the losing team that didn't eat a pin and look weak.
I am a believer if that both sides deliver a great match, winning or losing isn't the biggest deal. But, in this situation where WWE doesn't want either team to look too bad, how each team wins or loses needs to be handedled carefully. So, I undestand why WWE wants to do this.
I still think they could do match in the Chamber if they do it like War Games. Meaning two guys start out and once all six guys are in, the first man to score a pin or submission wins the match for his team.
IMO the real reason is to protect Cena from damaging his body even more right before his big title match with The Great One
If that's true, I can understand it.