Posted By:
Steve M."incentivized"? (I'll have to look that one up ) 
Seriously though, as they point out, this would be impossible to implement.
I've often considered one of the bigger problems to be the inconsistancy of grading. It is disheartening to have a lovely card graded SGC 30 and then see another card likewise graded SGC 30 that has wrinkles, tears, stains or what have you.
More training, quality control and over-sight of the actual grading process is where the companies should be putting their resources.