As far as FWD engines running hotter than RWD engines, I think the real difference is in the amount of air space around the engine. In a FWD car, both the engine & trans are under the hood & both generate heat (although the trans generates a lot less heat than the engine). Typically, FWD cars have more tightly packed engine bays than RWD cars.
An engine dumps heat to the surrounding air from all surfaces, but the amount of heat dumped depends on the temperature of the air. Cooler air will pick up more heat than air that's almost as hot as the engine. The more open space there is around the engine, the more air will flow and the cooler the air will be. Conversely, the more tightly packed, the more stagnant the air is, and the hotter that air will be. In a tightly packed engine bay, less heat gets dumped to the air around the engine, so the cooling system has to pick up the slack.
True, all of the heat generated by the engine eventually gets dumped to the air, but I think the real difference is in the quantity of air & thus how hot the air gets. Also, in a traditional RWD car, a lot of air flow escapes the engine bay down the trans tunnel & under the floor. The firewall in a modern FWD car is more obstructive to air flow, and I think it results in more air escaping out of the wheel wells.
My $0.02