Well, there's a few options here. If the blog owner wanted to host steem-based comments, then the only way to comment would be for the users to create a steem account and then comment. However, since this is just a website, the blog owner could also install Disqus or any other comment system to use on their site as well, if they don't want to force people to sign up for steem.

There's a number of projects in the works by the community that will hopefully make signing up for steem, voting and commenting a lot easier. We will be taking advantage of those new services as they come online :)