I'm sure there are standards like the ones mentioned, for me it's a question of "as compared to what?". I think of my huskies as medium-large.

Huskies are a medium-size dog (35-60 lbs.), but to people that own small dogs, they seem like large dogs. To people that own large dogs, (shephards, collies, etc.) they seem medium sized. I see quite a few dogs at the dogpark whose owners consider them medium (bassets, labs, pittie-mixes) that outweigh mine by a good 20 lbs, I think it kind of depends what you are used to.