there is no hypocrisy here. We have an API that gives users 100% access to all their content on Posterous, including the original media that was uploaded, in it's full size.
This API can be found here: http://posterous.com/api/reading
There is nothing stopping people from writing Posterous exporters that go to other services. In fact, Wordpress released a Posterous importer a few months ago.
We support data portability. It's the user's content, not ours. It's our privilege to host it for our users, and we are working hard to be the best service out there.
But I think it's also not about what users theoretically could do (if they were able), it's about making it as easy to get data out as you are making it to get data in.
If you did that you'd look awesome. Actively demonstrating that you aren't at all afraid of the competition could be as powerful as all the import functionality.
Frankly, the guys at posterous would have been big morons if they won't already have thought about it before starting their "migrating from dying platforms" campaign. It doesn't imply moral or ethics; it's simply business sense that when you are accusing others of something, you aren't guilty of the same charges.
The blog post to Tumblr users still rankles me.