nonsense. I typically worked at least 30 hrs a week while a full time engineering student. There were some semesters that I was TA'ing 15 or so hours per week and working another 20-30. Honestly I did better then because I was forced to focus on time management.
EDIT: I should add that a lot of this was by necessity because of American college costs...but I look at it as a long term benefit for me personally.