Well, music stands are usually only about 4 feet tall, so mounting a (big hairy old) mic in a shock mount coming up from below will usually block the sight line to the stand pretty much completely- you naturally look downhill at a music stand. Coming in from above lets the talent look right under the mic at whatever is on the music stand. If done right, it also encourages them to use good posture for the best vocal production (open stance, straightened throat, lifted palate, that sort of thing...).
Before the advent of cheap pantyhose, mics were positioned to *avoid* the pops- rather than stuck right in the middle of the pop path and then band-aided. Singing right on top of a LD condenser is sort of a modern perversion, anyway: in a good sounding room, you'd usually want to be a couple feet off the mic, in a classic big-name-vocal studio session.
If you haven't ever tried flying the mic in from above for a vocal session, you should. You may find that you can actually help out a less-practiced singer's vocal production, and get a better performance....