Ah right, sounddust's comment framed me into thinking there were no pictures of the iPhone 4 (searchable with the terms 'iPhone 4'), despite previous commenters pointing out they appear after several pages of results. Sorry about that.

But it does mean sounddust's explanation is incorrect, since this isn't a matter of whether 'iPhone 4'-searchable post-WWDC images are indexed. The question is why the images are buried beneath several pages of results.