My theory is that at least in the sciences, grad students are given an easy time in the course work because the Profs need them to do the scut work necessary to complete a thesis. We were basically serfs who generated the data for the faculty to publish. I was fortunate to have an advisor who was a tenured full professor, who wasn't under pressure to publish. He still got 5 papers published in refereed journals from my work.
This is a good general comment that describes pretty much every graduate program--not just the sciences, either. The toughest part is getting accepted into the program, and like you said, putting together the undergrad resume to be a qualified applicant in the first place and doing well on the standardized test. Thanks for sharing your experience.