While I didn't see this coming, now that I've been thinking about it for a while, it makes perfect sense.
There are some services that are used as launching points. Blogger is a great example. A lot of people use the Bloggers of the world as a no-fuss testing ground to get their feet wet. Libsyn is another example that a fledgling podcast might start out with just to get rolling. I know that I started blogging and podcasting with Blogger and Libsyn myself. After I realized that I wanted to keep doing both, I branched out and now run my own servers and software for both activities.
Back to iTunes. For major players that have enough traffic to their website to effectively deliver their own podcasts, iTunes might be used as a way to gauge audience reaction and growth. It appears that MLB and possibly Disney have found the outer limits of iTunes and are want to take control over their own domains and podcasts again.
The question is: will Apple care?