Well ... don't most users click on the first result, anyway?
So, clicking on the first result provides a great user experience (instant page: no wait).
Was there a significant problem with page load times to prompt the pre-load for the #1 result (which might involve more than one site, considering the amount of user-specific results filtering that is occurring)?
And, if the user continues down the page, clicking on results #2, #3, #4 ... which, not being pre-loaded, may have longer load times: is this creating a subtle, subliminal preference for the #1 ranked result presented?
Or, is this more smoke and mirrors?
When you consider the page 1 real estate is primarily text ads, together with that annoying cloudlet (which most users will never turn off), an increasingly limited number of sites are viewable above the fold. Google is masterfully controlling traffic and driving ad clicks.