A DigitalPoint Forums thread has an image of an AdSense ad that has the titles styled in italics fonts. Here is a screen capture from the forums, you can click on it for a large image:

As you can see, this is not the standard:

Several DigitalPoint Forum member said they have recently seen these ad styles around the web. So it appears that this may be a limited Google test and not a premium AdSense publisher modification.

Forum discussion at DigitalPoint Forums.