Let's begin with the reality 99% of Cardios ain't got a hint of a clue what welding is, let alone how it's done. Factor in that half of Cardios are primarily concerned with your dollar value to their pocket and the other half were in the bottom half of their class.
Fortunately, mine is in his 80s, owns a Lincoln SA 200, and knows how to weld. He also doesn't need money, so I consider him pretty honest. He's the one out of 4 cardios who told me I didn't need any damn electronic box.
The origin of no welding for people with pacemakers is derived from the habit of many ship and structural weldors to bring the stinger or TIG lead across their back, over their shoulder and down the arm to minimize the weight on the stinger or torch. This practice could induce sufficient magnetism into early pacemakers to change program or shut the happy box down. Ergo, no welding if you have a pacemaker!
Like all medical information and rules, once something gets started floating through the system there is no way in hell to stop it.
How many hospitals have you walked into and seen a sign No Cell Phone Use? How many times have you been assaulted by a hospital employee for using a cell phone. They don't need any reason, there is a rule. Guess what, most hospitals have given the cell phone rule up because people simply won't obey it..
As far as finding information on welding with a pacemaker, there is no manufacturer of welding equipment or pacemakers who will go on record. Both groups look to their insurance carrier who tells them to spew crap and stay off the hook.
Any pacemaker made in the last 10 years requires a specific instruction delivered via what can best be nomenclatured a transformer relationship between the coil in the device and the coil held against your chest. Chances of a welding machine duplicating that message may be impossible to calculate. Of course should you decide to take a couple wraps of 4/0 stinger lead around your body directly over the device, and run 800 amps to a 1/2" rod, you might be able to mess the device up.