Most blogs still run on shared hosting primarily for reasons of cost and a lot of people have existing shared hosting accounts that allow them to host multiple domains. If you're looking at individuals (the majority of whom are not typical HN readers and haven't gone down the PaaS path) installing this, it still makes sense to go LAMP.
Maybe within the HN ecosystem, but there are 10s of millions of wordpress installs running on the web. I would imagine only a very very small minority of said installs has any idea what a PaaS is. Those types of people are install wordpress on their $5/month hostgator accounts all day long because of stuff like fantastico making it a one click process as well.
Maybe I was unclear but I'm not asking to educate people about PaaS.
I'm proposing a button like [Create OStatus server]. It goes and provisions you a Heroku or DotCloud or Amazon account, creates an instance with everything installed, you get a link. Done.
We can make it way easier than installing Wordpress. The account provisioning part is tricky but all it takes is a good will partnership from one of the many PaaS providers, in exchange they get to upsell the owner to beefier paid servers.