I worked for Hyatt back when the first Grand Hyatt was introduced (Grand Hyatt New York, Trump's first big real-estate deal). Contrary to the OP, I would say just the opposite, that the Hyatt Regencies are convention/meeting hotels, and Grand Hyatts tend to be big, fancy hotels catering to business and upscale tourist travelers. But you're right, there's really little different in the rooms. In my experience, the Grand Hyatts (perhaps due to their urban locations) tend to have smaller rooms. The Grand Hyatt NY has a huge variety of rooms, but some are VERY small. The Grand Hyatt San Francisco used to be Hyatt on Union Square, not even a Regency in the name. I stayed as an employee, and was struck by how small the rooms were. I doubt that's changed any. The HR San Francisco has far more meeting space, though.