I would submit that self-reporting of calorie intakes is notoriously unreliable. I assume you didn't live with these guys and watch them eat every meal. From what I've seen in thin subjects is that they can eat a ridiculously high number of calories one day but then miss the whole next days - for an example. If they are consistent they will gain weight very predictably. It's like the obese people who claim not to eat much at all but hide Snickers bars under their pillow.
I do not believe BMRs differ that much.
JMHO. 
It depends on what you mean by "that" much. I have worked off and in with a guy for the past 10 years and he is now approaching 40. He is the epitome of an ectomorph, not a BB just more of a recreational lifter. In fact I would classify him as something else besides an ectomorph. The most this guy can pack on is roughly 15 pounds and this is with massive amounts of food and a cycle or two. He NEVER gains any bodyfat. I know that amount of food he eats and at best this guy will go maybe 190 at most. It may be lighter than that, but it has been a while since I have talked to him but when I do I can get more detailed info. Thru out the years his metabolism has not slowed down even a little.
On the other hand I have a friend who at one time was eating 10,000 cals per day at one point. Before any of you guys call BS I know exactly what he was eating and he posted it on here about 5 years or so ago. Anyway, I always told him that he was eating too much and that he was just stressing his body and wasting food. He was doing this when he was in college so he may have been around 22 at the time. All he did was lift, study and sleep, well and he was on the toilet a lot. This kid was going to the toilet about 6 times per day. It seemed that he was shitting out almost all that he took in. I remember that he ate tons of rice and protein drinks along with a lot of chicken. Yes he did gain weight, but he never got fat. His body did not seem to be metabolizing all of the food that he was taking in.
