Another thing to consider with Spolsky's student example is that there are a wide variety of experience levels in a programming class IME. I just finished 5 years of CS school (3 years undergrad, 2 grad), and I would attribute the variety in time it takes to complete a project mainly due to experience with the language/project type/etc.

There could be kids in the class with 2 years internship experience with the exact language on similar projects and those that have never programmed before.

Comparing professionals would be much more useful.