QDM requires hunters to pass 1.5 year old bucks, the same bucks which have the highest vehicle mortality rate. Thus allowing more 1.5 year old bucks to survive to 2.5. They will be one year "smarter", and more apt to survive to 3.5. This trend continues on, allowing more bucks to reach their maximum potential.
Everything I've read indicates that the mortality rate of adult male deer increases with age, it doesn't lower. The odds of a 4 1/2 year old getting to 5 1/2 is lower than a 2 1/2 year old getting to 3 1/2. As the get very old their chances of getting older drop off even faster.