I too would prefer a higher safety factor. I don't run it beyond 150 psi and I have a pop-off valve set at 175 psi.
The low safety factor has to do with the fact that these pressure vessels are meant to be temporary (or so I think). More information is available here
. These pressure vessels are meant to be (but aren't necessarily*) DOT-39 certified, which means they are generally not heat treated. DOT-39 certified vessels also can't legally be transported in the US after being refilled (I haven't read of that being enforced).
An ideal solution would be a heat treated slightly thicker cylinder. I'm not aware of any company that makes such a product, but if they did and marketed it right I'm certain they'll make a mint.
Here's some more info for those interested: http://www.catalinacylinders.com/lp.html
* The tank I have is NOT DOT-39 certified, but it was still designed to be a DOT-39 certified vessel. There's no legal problem with its transport, and as I mentioned, I use it at lower pressures than the recommended pressure, so it's very safe. The material is more brittle than it could be, but it's still aluminum.
All spud gun related projects are currently on hold.