App.net is a paid service. Twitter is a free service supported by ads. The whole premise of the article is that "Pixter is an ad-free photo sharing social network". Thats how we equate it.

We finish the article by "Over the last year, paid services like App.net and Posthaven have gained traction. Pixter is heavily inspired by these services, we want to thank Dalton and the team over at App.net for inspiring us."