There have been occasions when I was writing on something above my head, and the natural position to hold the pen in that situation is upside down. But these times are few and far between so I've never felt the need to invest in a space pen.
I have had those notebooks! And you are right...it is the ink (but superfine does work much better than like a "medium" tip for cheapo pens.) I just thought that if they can make one whose ink works underwater...they could make one that dried quickly.
When I was in college I did a lot of cocktail waitressing since it fit around my class schedule. Pens that can write underwater can also write on wet paper such as a running tab. Most other pens won't. Wait staff love that sort of pen!