I think the Bloomberg undergrad business ranking is kind of a joke. They have Penn (Wharton) at #16, and Villanova, ND and Boston College top 3. This just does not make sense no matter how one looks at it.
i student interested in a specific field will be much better served at a college that has a strong department in that field.
Yes most department rankings are about grad school, but they do measure departmental quality and this is something that trickles down to undergrad in terms of the quality of the professors teaching the courses, the quality of research opportunities, alumni network in that specific field etc.
The most reliable ranking system is the one that ranks my college and my childrens' colleges the highest.
This attitude may be more of a problem in business than other majors like CompSci that rely on provable skills (you might have graduated from MIT but if others in the company code better than you, you get cut down to size pretty quick).