I thought about this, but I wasn't able to find compelling data supporting the view that less prestigious schools have laxer grading standards.

Wikipedia's page on grade inflation says that the average GPA at Harvard during 2004 was 3.48, contrasting with 3.05 at UC San Diego. This is consistent with grading standards being roughly the same at the two schools.

Anecdotally, I haven't noticed much variance in grading standards for the same course across the ~4 colleges that I've had personal exposure to. I would guess that grading standards vary far more across different courses at a fixed institution than they do for a fixed course across different institutions.