I don't think any legal nonsense is involved at all, but I think the fact that WordPress.com keeps totally copying Tumblr features basically verbatim and now that WordPress.org is FINALLY getting what looks like some decent built-in microblogging support is indicative that Tumblr is more intune with how a lot of people blog now, and WordPress is more about general site/content management.

If doing comments and permalinks and whatnot wasn't such a colossal PITA, I'd have my own blog on Tumblr now. That's not to say WordPress isn't superior at many, many things, but Tumblr is easier, prettier and faster.

Hopefully the post formats feature will make this better.

But as I said on Mashable (http://mashable.com/2010/10/27/wordpress-tumblr-plugin/) -- for me the real key is the bookmarklet. Without the bookmarklet, a lot of the custom post formats stuff ends up useless.

Also, kudos to WooThemes for laying a lot of this groundwork, whether they get credit for it or not.