I'm probably one of the few who is actually more relaxed about table manners than her OH. My DH is almost obsessed with table manners, to the point where he has ruined meals with our (possibly dyspraxic) DD10, who still often uses her fingers to move food to her cutlery.
I'm American and so therefore my concept of table manners is automatically more relaxed from the get-go, though growing up we were required to use cutlery of course, not permitted to speak with our mouths full, not allowed to jump up and down from the table, not allowed to start eating till everyone was served, etc. But we also grew up with that (what seems to me now) really weird habit Americans have of cutting up all our food with fork in left hand and knife in right, then putting everything down and picking up with fork with the right hand to shovel everything in. One of my brothers bypassed all of that and doesn't even bother with a knife - he just puts a ton of force into cutting even things like meat with his fork, then picks it all up with his fork in his right fist. Even in my family that's mocked.
But my DH's very proper English family is on a whole other plane. Luckily I had moved abroad and adapted my way of eating to the "British/European" way of keeping knife in right hand and fork in left for the whole meal before I'd met him, or I'd probably have failed the first lunch his mother made for me. Meals were always served in the dining room with a perfectly laid table, crystal glasses, silver salt cellars, the works. MIL used to get extremely cross if people didn't start to eat as soon as they'd received their plates from her, because in that family hot food was everything, and it was considered an insult not to eat the food at its best. There's a bit of a hierarchy in serving people: little children first (because they were usually the hungriest), then "strangers", then "in-laws" (like me), then "family" with the "host" last. She never minded if others had finished before she had started. Table manners such as those discussed here were taken for granted.
DH therefore has a very overdeveloped sense of what is acceptable and what isn't at the table. He insists on cutlery being held in the "correct" hands and don't even think about putting elbows on the table. I kind of agree that putting elbows on the table looks slobby - for a few minutes of your day you can afford to sit up straight and show some respect to the person who cooked your meal - but the cutlery thing drives me nuts. As long as cutlery is being used I couldn't care less which hand uses it!
I think one of the drivers of etiquette/table manners is to draw as little attention to yourself in the act of eating (which is, let's face it, a rather "animal" activity 
) as possible. Another is, as mentioned above, showing respect to the person who cooked the meal. It's in that context that I enforce manners at the table. If my DCs are talking with their mouths full, it calls attention to the food, not the words. If they're eating with fingers it shows them behaving like babies/toddlers, not the pre-teens they are. If they're getting up from the table without asking it calls attention to their ingratitude for the meal. I'd be mortified if my DCs showed any of these traits eating at a friend's house. But if a friend (or friend's parents) shunned them because they ate with the fork in their right hand I'd say "meh. Good riddance."