I called CX USA Reservations and got the same answer as jrussell -- hotel provided on full fares F, J, and Y but not on discount fares including round-the-world.
If only I could get MikeFly's supervisor on the line! Could call repeatedly until I get an answer I like, then try to lock it in via some kind of written confirmation, but that sounds time-consuming and might not be successful in any case. (Plus, what if CX doesn't have so many reservation staff working, and I get the same person for a second time?!)
Mike, how did you manage to get the supervisor? Just ask the person who answered for a supervisor?