I liken it to the idea that the Infested Forest should look as dark and imposing as it is dangerous: replacing the craggily trees with candy canes and the wolves with golden retriever puppies (still trained to kill, mind you), and carefully laying a golden brick road through the center for easy access with a new sign at the entrance reading "Welcome to the Friendly Forest (Version 2.0)", makes a very dangerous situation look much less scary than it should... the "looking scary enough--or just being difficult enough to navigate--that you don't go in without an RPG party wearing enchanted armor carrying Ariadne's thread" was actually a feature, not a bug.
The real objective, I think, isn't to get everyone hosting their own stuff, but to popularize technologies that both allow data portability (you can move to another service), and are easy to use.
But WordPress has kind of already done this. They have step-by-step directions[1] for moving from a WordPress.com blog to a self-hosted install.
People who prefer Tumblr (an example of a blog host without an export function) to WordPress do so for reasons that seem orthogonal to data portability:
1. simpler, even easier to use,
2. aesthetics (sleeker design),
3. social networking features built in,
4. reach (because of #3, it's a lot easier to accumulate readers and engagement).
In theory, a service with an open-source codebase, or support for a standard export format, could provide all this. In practice, one hasn't.
Edit: icebraining pointed out downthread that you can mostly export a Tumblr blog by adding '/rss' to the URL of each page, a process that is easily automated.
[1] http://en.support.wordpress.com/moving-a-blog/#moving-to-wor...
This is one of the things the large hosts (Bluehost, GoDaddy, Dreamhost, etc.) are very keen on, and they've been doing lots of work to try and get this to a good level. It's one driving factor behind the push in the WordPress community to get automatic upgrades built in.
> Edit: icebraining pointed out downthread that you can mostly export a Tumblr blog by adding '/rss' to the URL of each page, a process that is easily automated.
In fact, WordPress has a Tumblr importer: http://wordpress.org/extend/plugins/tumblr-importer/
Notably though, it's built on their JSON API, not on the RSS, so it's not really an open standard.
I've thrown up a couple of basic WP installs on there in the past. One-ish click install and it Auto updates.
Lots of people run their own WordPress installations, but very, very few of them manage to do it well -- properly locking the software down, keeping the core and plugins up to date with security patches, putting the admin area behind SSL, etc. Which is why there's so many hacked WordPress sites out there.