Disclaimer: I work at Google.

This is not about analytics. This is just an experiment to test if using ajax instead of the typical form submit can make the result page load faster.

Here's an official statement -

  We’re continually testing new interfaces and features to enhance the user experience.
  We are currently experimenting with a javascript enhanced result page because we believe
  that it may ultimately provide a faster experience for our users. At this time only a
  small percentage of users will see this experiment. It is not our intention to disrupt
  referrer tracking, and we are continuing to iterate on this project.

http://searchengineland.com/google-ajax-search-results-death...