See http://googlewebmastercentral.blogspot.com/2007/07/supplemental-goes-mainstream.html

Apparently, Supplemental results have gone mainstream, From what I can tell, this means Google is now longer telling you which results are supplemental and which aren't – which I think is the wrong thing to do.

Other than making it more annoying for me to find out how my website ranks, there was something else I thought was interesting:
"Since 2006, we've completely overhauled the system that crawls and indexes supplemental results."

This has to be about the two crawler "system" from what I can tell.

I kind of like that they don't get too technical in search results, differentiating between different types of crawls and such. It only makes people worry too much about optimizing for Google's algorithms, instead of just creating great content (with the "official" W3C accessibility in mind).

I think the main reason for removing the tag was exactly as Philipp said, to make people concentrate on other things more. Specifically just building good sites.

>>people worry too much about optimizing for Google's algorithms, instead of just creating great content

Are you aware that many people can do both? So I understand that news really disappoint SEO & webmasters, but Matt is clever when, just in the same news, he said that pages in supplemental index will be more often crawled. An act of compensation...