You may think it's little more than show, but I don't. It has nothing to do with judging, it simply is something you are teaching your child or not. And asking the question, "Do you teach this to your child" is not judging. It's a question. The problem with this thread is people are acting like they're being judged and it's really just a simple question that got blown out of proportion.
I suspect one of the reasons it got blown out or proportion is that basic courtesy for others (eg. not smearing BBQ sauce all over the seats!) was conflated with fine dining etiquette, right from the first post. I didn't really take it that way, but I could easily see your first post being read as though people who don't teach their kids to spoon soup away from themselves, "properly" place their napkin, etc. are on the same level as those who don't teach their children to keep their voices down, leave other diners in peace, etc.
Veering a little...the napkin thing has always kind of bugged me. I'm a DD/DDD cup. I think I've spilled food on my pants about 2-3 times in my entire adult life, including barbecues and such. I used to spill food on my shirt about every other meal. If I tucked my napkin into the top of my shirt/blouse/dress/whatever, people would think I was a barbarian, but putting it on my lap, where I'd be protecting precisely nothing is "proper". It makes no sense to me. That said...my napkin stays beside my plate, unless I need it. I see it as a tool, not a prop.