The quality of other search engines has caught up to the point where brand is an important factor in the fight for search market share. Google's product is no longer clearly better than the alternatives.
Notice how most of the rest of the commercials on are for things like snack food, beer and cars where the image and consumer perception of the product are more important than the product itself. Those companies products don't do enough to differentiate themselves, so brand advertising has to do it.
This could be a sign that the search (really the information discovery) market is maturing and that product innovation will slow down as the major players focus all their attention on marketing and battling for market share. I hope not. While Google Search is good, it's nowhere near good enough yet.