I think people do take advantage of the pre-boarding.

I was on a flight once sitting in row 3 aisle. A lady came on board in a wheel chair. It was a relatively short flight. When the plane pulled up to the gate at the destination, the lady in the wheel chair just jumped right off her seat and grabbed her carry-on in the overhead. She then dashed off the aircraft in to her wheelchair as if she was running a marathon.

But what i thought was funny also is that the flight attendant that helped her put her carry-on in the overhead when she boarded comment to her "you sure are fast on her feet for someone who came on with a wheelchair".

I then told the flight attendant "your comment was right on and also funny".