[gizmo686]

No student learns everything that university teaches; there is simply not enough time. It would be ideal if each student received a perfectly customized curriculum; but that is simply not practical to do. Instead, universities have a modular system; where different students can mix and match modules to cover what they are interested in. Similarly, different majors can mix and match required module to cover the material that is nessasary for said majors.

In the case of subjects with a very large number of students, it is possible to produce specialized modules, so you might have a university offer a separate probability-for-scientists and probability-for-mathematicians classes that it considers to be interchangable, but differs in how it covers the subject/what background it assumes.