Without commenting on the validity of the argument, the point that you're missing (not your fault, the post wasn't clear) is that there will be separate ("siloed") G+ instances for these universities. The distinction will be the same as Googlers having access to both public and internal/corp G+.

One use case for this is that I can make a G+ event (e.g. a party) public, and know that only fellow students will see it.