It is always the fault of a party changing the oil....but the poor guy who ends up with the stripped thread may not be tha same one that did the damage. It could have been a prior gorilla.
I've been changing oil for over 40 years and never stripped or cross threaded a pan. Some would say I'm lucky. Some would say I'm smart. Some would say I'm weak. I say I take precautions. I only use "stubby" wrenches to install plugs, to limit the amount of torque I can apply, I clean the plug and thread before reinstalling, and I take the time to be sure the threads are properly engaged. If it isn't starting smoothly, I back out and try again.