Kris, there's any amount of dumb "etiquette" stuff out there. Seriously, I remember seeing a program with some stuff shirt saying the polite way to eat grapes - you don't strip them off the bunch, you cut a small branch off the bunch with (and I kid you not!) a pair of grape scissors, these being scissors designed for cutting grape stems!
Next time anyone complains about lack of old-fashioned manners around me, I'll start eating with my hands and throw the bones over my shoulder. You want "old-fashioned manners", that's what you'll get... ;-)
There are practical aspects to some things - for instance, eating with your elbows held at your side makes sense, cos when you eat at a canteen (at work or school) you'll be unpopular if your elbows are whacking the noses of your neighbours! Or restraining farts in enclosed environments such as lifts. But if there's no relevance to it, then why should anyone bother?