as stated above, obviously, the #1 reason for tube mics is b/c in the past (meaning "historically"), over a couple hours the tube would get hot and could warp the diaphragm. that's not an issue with non-tube LDCs, and IMO, there are two "big reasons" with non-tube LDCs.
1. it's easier to aim the mic "down". this emphasizes the "chest voice" and minimizes the "head voice" (and the associated nasally tonalities). generally this is a good thing--unless, of course, you want to emphasize someone's nasal qualities.
2. it causes the singer to lift their head--thus straightening the throat and clearing a path for better singing posture and projection (and thus hopefully better tone).
even though i can "aim a mic downward" just fine when it's "right side up" on a stand, i've found that i get better results when i flip it over. plus, it's out of the way of the music stand. AND it "looks cool", and where clients are concerned, looking "cool" or "professional" often elicits a better performance out of them, and all else equal, a better performance is key and i'll do whatever i need to in order to get that.
personally, i haven't noticed any "reduced proximity effect", but i HAVE noticed i don't "smack my head on it' as much.

:b
cheers,
wade