aJillSandwich: Given Steam's new refund policy, I'm surprised more of these games haven't added a requirement for the Steam client to be running. When the refund policy was announced, I just assumed, "No more DRM-free Steam games" but that hasn't been the case.
I think the majority of people that might be interested in abusing the refund policy in this manner probably already have alternate sources for obtaining their games for "free", and which they consider more convenient to use. I could be wrong, of course, but given some information I've seen floating around with respect to refund rates hovering around 1-2% for most games it doesn't seem to be too significant an issue... and hopefully it will stay that way!