It depends on the hotel and the guest. I've reserved two rooms of 3 registered guests each (total of six) and had breakfast for 6 written off - at Parks and Andazes, and I've been nickel and dimed at Regency's when I registered 2 of us and did the buffet.

Strangely, I've found that the "better" the property, the less of an issue breakfast is, especially if I've stayed there before. Breakfast at the Blue Duck (PH DC) is really really good, and I've never seen a check, even on points or award stays. Of course, it also helps that we dropped 1K on room service and dinner (meals on 2 separate nights) the last time we stayed, but we have been before on points and basically only paid for the valet and still there was no breakfast bill, for 3 or 5 on separate occasions.

If you are on a Diamond challenge, I tend to think that on the one hand, they might actually treat you really, really well in the hopes of keeping your business, especially at a decent Park Hyatt, whereas at a generic property, your mileage is really going to vary. I have to laugh because I think about the guy on the other thread who wants to do the diamond challenge so that he can get breakfast for 15 days in Europe, after which he will not stay again. While that is Hyatt's fault for offering the challenge and all it brings, those things can't be ignored by the staff at some properties, I imagine, like the PH Vendome. So, I guess that it's a long way of saying that if you registered the max number of guests in one room, then you should get breakfast for all in that one room. Sometimes, you may get more. Email the property if you are so worried about breakfast. Usually, they will tell you, and then you have it in writing.

International property - usually, it is the number of registered guests in one room, which is why max occupancy matters, and why they ask for the number of folks staying in the room and adjust the price of the reservation itself. Park Hyatt Tokyo, up to the number registered, which is why the price changes depending on the number of guests. Same for Paris and Milan and Zurich. If you bring in a guest and go over, you will pay. Not a cheap date in Tokyo or Zurich.