As others have already noted, it can happen if you have status, with better benefits for Platinums than Golds. Nevertheless...

FWIW, as a Gold I've had this in the past few years at the wonderul Le Meridien Khao Lak in Thailand, at the grand old Bristol in Vienna and IIRC at least one or two other spots. Award stays in a junior suite at LMKL and in a regular room at the Bristol respectively upgraded to a much larger regular suite and a very special suite at those two properties. It probably helps to write ahead very politely asking (and not demanding) the upgrade if available, pointing out any special occasions such as a birthday or anniversary coinciding with the visit. And don't expect the upgrade, since that can put a damper on one's stay if it doesn't happen.

In my limited experience, this kind of thing happens more often and the nature of the upgrade is better at overseas properties rather than US ones, but others may know better about this.

You might find more examples of such upgrades on award stays at the threads here discussing Platinum and Gold upgrade experiences.