While you can debate how well CM3 matches up to past DPOY winners, you have to compare him to his competition from this season. (Polamolu, Wake, Harrison, Peppers, Revis)
For me, these awards must take into account a few things:
1. How well the team did.
2. The players stats.
3. What the team would be like if that player was gone.
With these in mind, I can't say that any other player deserved it more.
The Packers finished with a good record and a great defense (that removes Cameron Wake from the discussion).
If you look at stats alone. You can safely remove Harrison (10.5 sacks) and Peppers (8 sacks)from the ballot.
If you look at the value that the player had the team, The Steelers D allowed 14pts a game in the games that Polamolu played in and 12.5 in the 2 games he missed (granted 1 game was against the abysmal Panthers). Revis had down year, and the Jets D did not crumble in the games he missed (they won all 3, allowing an average of 22 pts.
When you look at Clay's importance to the Packers, it becomes more evident. He was injured early against Washington. The Packers lose that game by 3pts, the lose the next week against Miami by 3 pts, both games in overtime. The Packers D get 1 sack during the time that CM3 misses and, if anyone remembers those games, our pass rush was non-existent.
So basically, I can think of no player who deserves this award more than Clay. GO PACKERS!