It's up to the team to manage their roster though. Some teams do carry 3, others don't. I don't think it's too risky to only carry 2. The likelihood of both getting taken out in the same game is pretty slim, but it's a risk they take to add depth elsewhere.
I hear ya... just think it would be better for the game if the league just let the teams carry a third QB and not have to give up a roster spot. There are plenty of times in a season teams lose two QB's. Why not have a third on your roster, getting practice time, learning the system instead of having to grab someone off the street to start from scratch. I guess by that time the teams season is blown, so who cares anyway.