I just changed the url of one of my posts from

http://2011.denmark.wordcamp.org/session/theme-frameworks-trends-og-standardisering/

to

http://2011.denmark.wordcamp.org/session/wordpress-themes-mere-end-design/

Now, if I go to the old url, I get redirected to the new one! This is great of course!  ...But is this a feature of WordPress, or what's going on here?

Does WP keep track of a posts url history, providing rewrites/redirects for former urls? Looking at the response header I see WP is sending out a SEO friendly 301 redirect.. YES!? I thought I'd have to set up those redirects using rewrite rules in my htaccess, so I'm curious to know how it happens that WP is giving me my new url when I type in the old one here..

Any light on how WP handles this would be appreciated.

I just changed the URL of one of my posts from

http://2011.denmark.wordcamp.org/session/theme-frameworks-trends-og-standardisering/

to

http://2011.denmark.wordcamp.org/session/wordpress-themes-mere-end-design/

Now, if I go to the old url, I get redirected to the new one. This is great of course! 
...But is this a feature of WordPress, or what's going on here?

Does WP keep track of a post's URL history, providing rewrites/redirects for former URLs?
Looking at the response header I see WP is sending out a SEO friendly 301 redirect... Yes!?
I thought I'd have to set up those redirects using rewrite rules in my .htaccess, so I'm curious to know how it happens that WP is giving me my new URL when I type in the old one.

Any light on how WP handles this would be appreciated.