this is indeed true, however with POSSE instead of PESOS you can still post new content if the external services are down, and your copy is the first copy which existed, meaning you can link to it from syndicated copies, which enables all kinds of cool stuff like http://indiewebcamp.com/original-post-discovery
That is the essence, yes :) We’re trying to take a different approach to previous federated social web efforts, and focus on bringing existing UI, conventions and technologies from blogging up to par with their silo equivalents.
My personal inclination is to accept any comments from people I know, and notify myself of any from people I don't know. I can then approve them/block them by adding them to my address book.