[wp-hackers] Why WP_SITEURL and not $_SERVER['HTTP_HOST']?

[Mike Schinkel]

Hi all,

I've been wondering this for a long time but never asked this.  Anyone know why WordPress doesn't just use $_SERVER['HTTP_HOST'] and instead requires setting of WP_SITEURL (and WP_HOME?)  

There's obviously a good reason why it wasn't used, right?  I'm trying to write a plugin to switch domains and I'd like to know if there are cases where $_SERVER['HTTP_HOST'] is unreliable?   Anyone know the history and rationale?

Thanks in advance.

-Mike