The secret to having auto strafe on is that pressing the R trigger makes your player not strafe while defending the crossing routes and whatnot.
The change makes total sense because before (Madden 10 and under) most of the time on D you spend strafing waiting to react to a play. This means you are holding L most of the play just to keep your player in the spy position (facing the QB) until needing to break on the ball (by letting go of L and sprinting to the ball carrier). With autostrafe on, you don't have to hold that L button waiting for something to happen, it does it automatically making your player slower and keeping him in position to break on a ball with the R trigger like in previous years. The only difference is that you don't have to hold that L for a bit.
What do you mean when you say "break on the ball with the R Trigger"???
Can I tap the R Trigger while the ball is in the air to "break" on it???