Nail in tire, Repair or Replace

As a kid, I hung out with my grandfather a lot when he worked on things, and he always plugged holes in tires. Never had any trouble out of them all those years. Well, of course, I picked up that habit and always plugged mine. Well, not long ago, my wife ran over a screw on her way to work, so I plugged it and she went on to work. While at work, the tire had lost a little air she said, so I told her to take it to a local tire shop and have it patched from the inside. Wasn't long and she called me to tell me that since I had installed a plug in it, they wouldn't patch it due to liability. Called several local places before I finally found a privately owned tire shop that was happy to install the patch after I had plugged it. I must assume someone, somewhere must have had an issue with a plugged tire, sued, and won a lawsuit. Now some chain stores won't touch a plugged tire. Not sure if this is something going on Nationwide or not, but thought I would toss out the info just in case. Oh, and yes, the tire is on another of our vehicles, and have had no problems with it.