Propane tanks also used to have backwards screwing connections. I believe this was a safety 'feature' given the mainstream use of small propane tanks. Having them tighten counter-clockwise prevents similar looking but wrong hoses from being attached to the tank. It also tricked people who didn't understand propane tanks form being able to remove a connection (since they would usually just tighten it further).
Cars generally still do have backwards nuts on the LHS. Something about vibration and direction of turn. Some of the other bolts on the LHS can be that way too.
Same with some of the LP gas cylinders I have encountered here in Aus.
I have heard that other manufacturers originally starting using reverse-thread propane fittings to work around a 1896 Primus patent, and the situation has simply persisted.
http://en.wikipedia.org/wiki/Lug_nut#History
Propane tanks also used to have backwards screwing connections. I believe this was a safety 'feature' given the mainstream use of small propane tanks. Having them tighten counter-clockwise prevents similar looking but wrong hoses from being attached to the tank. It also tricked people who didn't understand propane tanks form being able to remove a connection (since they would usually just tighten it further).