Natural gas piping is done at such low pressures in residential environments that it's basically a joke. I think it's about 0.5psi (or 14" of water column) which in the grand scheme of pressures is very low. People can generate greater pressures with their lungs.

http://hvac-talk.com/vbb/showthread.php?1587361-What-is-typi...

http://www.personal.psu.edu/ref7/apparatus/2003%20competitio...

EDIT: I'm not saying that one should do their own natural gas piping as in many places it's technically illegal unless you're a licensed plumber. But it's certainly not rocket science. The only reason it's "harder" than plumbing compressed air is that if compressed air leaks a tad, it's no big deal. You have to get rather tight on gas piping because of the consequences of a leak, not because it's so difficult to get it tight.