You have a good point - the different blogging platforms do a good job. And create virtuous ecosystems around their code in the form of theme creators, hosting providers and consultants.
I think Kenton is onto a winner with Sandstorm - it stands half a chance to actually unify different blogging platforms. So while you may use a different blogging tool and comment - you have a unified email-like identity that follows you between tools, nodes and networks.
I'm doubtful about how long Sandstorm would be able to stay strictly hands-off. Sooner or later everyone who allows random strangers to interact has to get into policing the content and that's nobody's idea of fun.
I think Kenton is onto a winner with Sandstorm - it stands half a chance to actually unify different blogging platforms. So while you may use a different blogging tool and comment - you have a unified email-like identity that follows you between tools, nodes and networks.