First off you have to remember that the bigger you are, the more calories you will be burning to sustain life in general, to digest food, etc etc. So in a sense, that's going to be part of the calculation. A 300lb person is going to be utilizing more calories per day than I am. Its going to boil down to overall calories.
Feed a fly a minute piece of meat and it will live. Feed a dinosaur 1 4oz chicken breast and see if it lives. See my drift. Of course they aren't lifting but you get what i'm saying.
You know as do I on here you'll here the 2g rule, and you'll have your people who will tell you I dont preach the 2g rule, and they are correct. To each his own, but I dont follow a 2g/lb rule and i'm not a fat dude.
I personally believe the 1-1.25g/lb is fine. And i'm not going into the whole argument about protein since i've exhausted it, and I dont care to debate protein requirements since there is no data to suggest otherwise that 2g does anymore than 1-1.25g does. The ONLY data people have is they say... Look at so and so. Comparing a person is the worst thing you can do because of so many factors that contribute to size or mass or what ever. You cant justify yet saying so and so takes 2g so he is bigger. Because then you'd have to debate the fact that from 1-2g, that is also DOUBLE the caloric intake as well. Then its proving it is SOLELY the protein and not the extra calories.
Endurance exercise alters protein metabolism and increases amino acid oxidation leading to increased protein needs. So in short, yes, if they are doing tons of aerobic exercising they still need it. Not as high, but close. I dont think you can put an exact number on it just like you cant with weight training.
I guess too, define what you mean by fatter people? Remember as well, you are going to gain muscle if you lift. Doesn't have to be bodybuilder type, but strength training (lifting) will do that. Its not possible to lift and not gain some type of additional muscle.
Maybe this isn't what you are after, but I wish it was simpler than it is, but truth be told its not. Get into detail in a exercise phys class, and then watch your brain work overtime. There is so much beyond what we all discuss here, it will make your head spin. This is why there are so many unanswered areas.
Just as a point, we all talk about muscles, but have you ever taken a look at the muscle in a book? The whole thing broken down, then the whole process of contraction and relaxation? SO MUCH is involved in a step that takes 3 or so seconds. Same with your question.