I agree with the idea as well but also to a point. I think having business experience will definitely help you connect the dots and see the big picture of the classroom material and theories you will learn. I also think that having work/business experience will help you realize what you are interested in and want to focused on, drawing what you want from a program for the short 2 years that it lasts. I've heard that the people who get a lot out are those with a good idea of what they want to do and how they want to spend their time so if they don't have work experience a student may want to try it all.
I don't think there is a science to the perfect business school experience. You can still try new different things at bschool and succeed but I think having experience can bring maturity, understanding, drive, and focus that will be valuable in your business school experience.
From a profs experience I can see why he thinks part-times are getting more from the class because the part timers don't have to recruit. That allows the part-timers more time to spend on classwork and interacting with the professor creating a prof biased. I'm not sure which is better but there is more to bschool than just the classes.