I’ll mention (for the 3rd time) that you don’t need a dedicated site or server to run the Update Manager. If you don’t want to use it for other reasons, that’s fine – but, that’s still not a valid reason.
Yes, CP needs its own update mechanism. However, releasing plugins to be used in production environments without any ability to update is irresponsible. If you inadvertently introduced a vulnerability in the plugin code, the users would be stuck with it and have no way to even know it existed until they got hacked.