Icons of beta sites are different form the icons given in the http://stackauth.com/1.0/sites . As example:  
<blockquote>
Original icon of the <a href="http://english.stackexchange.com/">English Language and Usage</a> is<br />
<img src="http://sstatic.net/english/img/favicon.ico" width="30" height="30" /><br />
where <a href="http://stackauth.com/1.0/sites">http://stackauth.com/1.0/sites</a> gives the icon<br />
<img src="http://sstatic.net/skins/sketchy/img/apple-touch-icon.png" width="30" height="30" />
</blockquote>
Why?