One of the things vertical rhythm's used for is making two parallel columns of text align with each other at regular intervals. From my limited knowledge of music, every measure of a song, the song's elements align. In a design, every measure (baseline), the design's elements align. By align, I don't mean with some arbitrary measure, but with the other elements.

Here's a quick example I made: http://i.imgur.com/NEc92.png

You do make a good point: When you get into single-column layouts, like a solo in a song, having mathematical vertical rhythm is irrelevant.