The more OAuth providers there are, the more inconsistency there is. Not following the specification puts an increased and unnecessary burden on the developer.
In the past couple of weeks I have coordinated and authenticated with more than my fair share of OAuth providers. That being said, you should be thinking "Hey, isn't OAuth a specification?" Once you do one you should be simply swapping out keys and urls and you should be good to go right? So wrong.
Follow the specification and be consistent.
This article is meant to let the OAuth providers know some of the pain points of dealing with them as providers and steps they could take to make interacting with their API a joy.