The difference is who owns and pays for what. Running a centralized application for more than a few people on donations and goodwill is a challenge.

This is why I am a huge fan of distributed and federated networks. The idea of you and your buddies being able to split a dream host subscription, but instead of being locked into your own forum hangout, you can interact with a whole global network of fellow self posters and VPS renters. We are in the early days of high-quality federated interaction for non-nerds, but we will get there.