A lot of teams play better defense without a great shot blocking center. So it's not just Lopez.
Here is an interesting stat for Lopez, it measures opponent FG% at the rim. I filtered it for players who average at least 1 block per game. Lopez is at 46.5% per game....the really elite defenders like Hibbert and Davis are at 34-35%. Lipez is 22 on that list, but higher than players like Drummond, Dalembert, Ibaka, Gortat, McGee, Jordan.... McGee and Jordan's % is particularly bad.
http://stats.nba.com/playerTracking...=FGP_DEFEND_RIM&sortOrder=ASC&filters=BLK*G*1