A Scholarship midshipman has to have both calc courses and both physics courses done before his sophomore and junior year (respectively) to keep the scholarship. Its much, much harder to pick up the scholarship if you aren't tracking with the scholarship middies.
Agree with raptor, doing the calc and physics makes your scholarship package much more competitive. It isn't a requirement, but when the Navy is being stingy about giving out scholarships, even small things like that can set you apart. If you do pick up a scholarship while on college program, you won't be held to the same calc and physics requirements that the 4-yr national awardees are, so at that point in time there is no need to continue unless it is required for your major.
HD