Because, with the current proposed architecture (built on http), In order for your friends to access your content your server must be online, and most computers not dedicated as a server at the very least sleep periodically during such periods your information would be unavailable, thus the need for dedicated servers.
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Why can't everyone host their own seed? If it's a binary I have to install and download and message propagation is done in a p2p way?
Because, with the current proposed architecture (built on http), In order for your friends to access your content your server must be online, and most computers not dedicated as a server at the very least sleep periodically during such periods your information would be unavailable, thus the need for dedicated servers.