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.
1. http://smarterware.org/8026/why-not-tumblr
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.
[1] http://www.tumblr.com/docs/en/api/v2 [2] https://github.com/mojombo/jekyll/blob/master/lib/jekyll/mig...
If RSS went all the way back to the beginning, then you'd be right, it would get you 99% of the way there.
It'd be nice if they supported <link rel="next"> tags, but it's still extremely easy to dump the content.