Exactly. There will be sampling bias. Opera in particular makes it very easy to turn off sending referrer information (one click on the quick preferences menu), so Opera will be underrepresented in any data corpus derived from the referrer.
Or worse, Opera users will change their user agent string to Mozilla so as not to have to deal with ua-sniffing websites that work fine on Opera but warn you anyway about using a unsupported browser.
I saw the story, but didn't click the link. So it's definitely not going to match what pg and team see when they examine their logs for actual HN Readers.
