Originally Posted by
missinglink
Are they known to be available on tubes other than 700C road tubes?
Sure - tubes for folders and recumbents in 16" and 20", tubes for MTBs in 26", all available in presta, probably even your choice of stem length. I'm surprised your guy had 20" tubes and didn't know they were presta though... definitely not the standard, so unlikely you'd get them off the shelf at the LBS by accident.
Another Schrader problem: I had a Schrader valve get hot and leak on a long descent on my tandem - somehow the spring check just got hot and deformed or something. Made the strangest whining sound and then I had a flat. Can't happen with presta.