Well, I don't know how the Reddit API works, but what you described is generally bad practice, as is my understanding. The Oauth token's allow the app to perform actions on the behalf of authenticated users, but they still need to use the reddit API, and I imagine an API key, to perform those actions. You generally aren't supposed to use Oauth as a access authentication mechanism.
At least pricing is per Oauth key, but still, the pricing burden is still going to fall on the developers for these apps who reddit now views as their "competitors", despite making a product that supported reddit's business for years.