Robert_Charlton - 12:49 am on Sep 17, 2012 (gmt 0)
I'm just guessing here - but I'd say that when lots of pages show up from the same domain that's a sign Google's algorithm doesn't feel there are very many quality results.
I agree. If Google is finding that, in the top 10 pages (100 results at 10 per page) for a query, that it's getting 75% of its user engagement on say, 4 domains, does it give those sites 8 listings in the top 100 results or does it test by displaying more and see what happens?
Different types and displays of sitelinks were one type of variant that Google tried... Sitelinks, Mini-Sitelinks, Mega Sitelinks, etc. It could be argued that those attracted more attention than multiple results might... and that host uncrowding was at least an alternative which the data more or less forced Google to test.
In terms of what Google's been doing, btw, it's most informative to view these results 10 per page, as I'm guessing that's how Google's been testing them. It's most likely getting much more searcher data from the top 2 or 3 pages, and less so far deeper down... so I believe I'm seeing the most granular changes occurring on those top pages. I'm guessing also that as Google gets more data it will make more changes.