Also, Blogger, the service that the link in the paragraph "... publishing tools that epitomized all of these traits..." was referring to. Or, more modernly, Tumblr. These are all sites that give you your own [sub]domain, where you make the rules and you control (almost) all the data, and where, even if there are other mechanisms for connecting things together, you can still just pull an RSS feed of all the relevant content and mash up whatever you like.
I wasn't aware that Tumblr had an export function, and it looks like, officially, it doesn't[1]. There is a third-party migration tool to WordPress[2], but that's about all I can find. So unfortunately, not all is roses.
It would be nice if there were a standard format for storing blog posts and their metadata and attachments, so you could move from anything to anything. Perhaps the nascent Tent protocol[3] could do that when it's mature.
Tumblr has a JSON API [1] that is fairly usable, and provides access to the essential parts of blogs (and terms of use explicitly allow building data portability applications on it, which is a nice touch). It's not instant-export, and I get the impression nobody uses it so it might not be rock solid, but if you need to export data, it's possible.
This tumblr2wordpress tool is probably built on it. So is Jekyll's tumblr importer. Honestly, the lack of export tools for Tumblr probably comes less from a lack of demand than anything else.
