While it may not be a banner ad, it's a foot-in-the-door technique. Display these branded search for a few years, so when they're ready to implement real banner ads, users won't be shocked.

Just imagine the press release.

"This isn't something new we're doing. We've been experimenting with showing users highly targeted banner image when querying for specific terms. We're only expanding that target to help users find what they need faster."

Bam.