WRT the LP
All plumbing I have ever seen that was intended to be used for gases has had left-handed threads.
The reason: Simple - so you don't accidentally use a fitting that was specced for water in your home's natural gas line, thus potentially causing leakage (gas fittings are higher-quality) and eventually blowing yourself up.
Yes, corporations feel a need to protect people from their own stupidity. That, or it's a CYA thing, I'm not sure..