Exactly!!!
You give a cushion to prevent the WR from just running past you for a big gain. The thinking is that by giving up only short gains that you will make an offense have to run 8 or 9 plays to score and that at some point they will make a mistake that you can capitalize on (fumble, tipped pass, ect...).
The downside to this style of defensive play is that you normally dont get alot of interceptions since teams basically take the short passes that you are giving them. Also, if you cant generate any pressure with your normal rush packages, you will get ripped to shreds playing this style of defense.
Which helps to explain why we are the worst team in the NFL against the pass. (303 yds per game, ranks us at 32nd according to NFL.com).