In any event, the only way I can think to do this with an ajax search is to pass every outgoing link click through a redirection script, so that the referrer is rewritten to something useful.
However, whilst improving things for webmasters, that would seriously negate the point of using ajax, and be a pain for end users.
Google are serving their end users. I don't think trust comes into it TBH.
What would you rather google do? not progress and use ajax search, or use a redirection and make a worse experience for end users?