I don't lock only the wheel, either. I put my u-lock around the seat-stay, a couple spokes and a portion of the rack. That's why I park on the end, like that.

With a long cable lock, like the one used to secure the bike on the right, you have even more flexibility - that bike could have been parked with either wheel inserted between the vertical posts, and the cable routed through the frame and around the rack. Or the bike could have been placed outside the rack, on the right side, and secured to it. There's no need for anyone to park it that way, unless they're just lazy, inconsiderate, or aren't smart enough to figure out alternatives.