It would be interesting to know whether or not the OP booked a guarantee or a specific cabin and if he went through a T.A. or not.. I've always said upgrades are not all that people make them out to be. Moving up one or two decks to the same cat. cabin isn't an upgrade to me and too, you have to be very careful where the so- called upgrade puts you--under the galley--under the show lounge, under / over the disco, etc.
I always book a specific cabin and have had one upgrade to a suite but I was asked well before cruise time if that was acceptable. I checked the location of the suite and accepted the change.
I don't see how when you have booked a specific cabin that upon check in they would just automatically announce a cabin change unless there was a problem with the cabin itself such as a/c, plumbing, etc.