[JohnTHaller]

Many sponsors and partners will not accept log-based self-hosted stats as they can be easily faked. Many will only accept a 3rd party stats site like Google Analytics as they can be provided with a read-only view into it and know that the underlying data isn't faked. It could be gamed, of course, with some effort (botnet of IPs loading pages from the site, etc) but it's much more involved than faking a Piwik report. Of course, many of the blocklists that block GA also block self-hosted Piwik anyway.

There's sympathy for ad-supported sites because that's the vast majority of the internet's content. And micropayments, paid memberships, etc have almost universally failed with the exception of a few very large publishers and a few very specific niche publishers.