Foo! In this case, I was really, really hoping you were right and that there was an actual difference between our accounts, which would suggest something being rolled out already.
As I said... Sadness.
To me this has always been the second greatest, most useful feature of Google (after web search). Yup, I use image search, Google Analytics, Gmail. Maybe some others that I don't recall, but I was perfectly happy without them and, to be honest, I wouldn't really miss them that much. They all have reasonable equivalents.
Customized book search was literally something on my mental dream list for years (I'm a historian, right?) and when I finally got it, I couldn't believe it. Now that it's been taken away from me, I can't believe it either!