Funny enough, realistically, you don't really see someone's teeth through casual interactions. It usually takes a good laugh, big smile, etc. to get someone to show their teeth and even then, unless they have a lot of issues, you won't be able to tell if someone has messed up teeth, honestly.
As far as noses go, I think people just underestimate how annoying noses are to draw and that simplifying them is a practical solution, especially in animation when you gotta be able to copy that nose design from drawing to drawing.
Some shows pull it off better than others, but I'm not surprised when noses are kept more conventional.
Is Tumblr into forcing the 5 finger rule on characters yet? That would be fun to see actually.