Outside the United States, most airlines tend to (a) have carry-on rules and (b) enforce their carry-on rules.
Inside the United States, it is not unknown for the airline to (a) allow virtually anything on, regardless of rules, for the first 50+ passengers and (b) thereafter force you to check cameras, etc., because their luggage racks are already full of stuffed Disney toys the size and weight of a small child.
The only other area I know with the same flexibility (and they are usually more realistic) is the various airlines of the Near East/Persian Gulf.
R. (Who once had to check a 4x5 camera for this very reason)