This was noted as a test in 2008 but today I am seeing the Display URL before (i.e. on the same line as) the Description text in the ads that appear at the top of the SERP. I am using Google.com.au. (I also got it in Google.com)
I couldn't see it mentioned recently, so apologies if this is old news. I find this layout untidy.
I believe the Google featured/top ads always had the display URL on the same line before the ad description. I am confused. I have screen shots from the past years, dating back to 2004, showing me this.
In 2008, Google was testing this with the normal ads (ads on the right side) and that was new. But you are saying the featured ads at the top of the search results.
It's not that top or bottom is better, it's just a little different, which brings some attention from long-time users. This is basic advertising that applies to TV, print, billboards, radio and even Google. It's a good idea. Consumers don't like big changes--they find that to be confusing. But just a little tweak can perk up response.
There is a beta program that hooks up Google merchant account to AdWords ads that just shows a short product description, display URL, and an image.
It is not a product extension; it's different and you can spot the difference as there's not a + sign to expand the ad and view the product extension images - these images are displayed directly on the search page.