There are two advantages to the Aadvantage program over the Skymiles program.
1) You're right about Q-POINTS, but you can also qualify on AA by segments and by actual flown miles, for Gold and Platinum (equivalent to DL's Silver and Gold). However to get the Executive Platinum (equivalent to DL Platinum) you do have to qualify with Q-points.
2) When stuck in coach on AA you have much mor elegroom than on Delta's coach product.