Oh it's definitely the case in North America too. Comedy is hard and you can't do it all without an audience, so the quality at open mics is always going to be mostly terrible. Same with any artistic endeavour really, but in most things beginners can just bumble along in private. Not so with comedy. If you're into learning it, I would really suggest a course with enough people that you get a semi-private open mic every week. It's a great way to test material on a semi-realistic audience. I've done a couple here where 2/3s of the class time was our private open mic, like a comedy version of toastmasters, and that alone was worth the money. (Hell, given you have to buy at least a drink at an open mic, it wasn't even expensive!)