lammert - 2:58 am on May 23, 2010 (gmt 0)
I didn't run extensive tests yet, but the Google referrer missing appears to be a browser issue rather than a Google issue. Most browsers block sending a referrer to a HTTP page if the source page is HTTPS. This can be circumvented by offering your site via SSL rather than unencrypted.
SSL certificates start somewhere around $20 per year, which isn't much for any decent money generating site where the webmaster wants access to the referrer info in the server logfiles, but it is a massive investment for all those domain parkers, typo squatters and other borderline Internet entrepreneurs who rely on domain quantity rather than quality. Instead of a few dollars per year for domain registration they now face a minimum $25 investment per domain if they still want referrer info for their sites.
This may therefore be a clever move of Google to separate the legitimate Internet businesses from those who try to cheat.
After all there is no technical reason anymore to not serve all websites through SSL, except for the one IP per site issue. A few years ago server side CPU power was still a limiting factor, but with current multi-core processor setups most websites are limited by harddisk and network bandwidth now, rather than CPU power.