Go back and review Jim's post. In fact here is a great thread that he started: http://board.CrossFit.com/showthread.php?t=41555
Go read through that when you have some time.
You know why dairy helps with mass gain so much? Because the protein in dairy, unlike most dense protein sources (read: animal meat), has a rather potent insulin response as opposed to the typical glucagon response.
Yes in fact you can. Do some research. Your body will fight to maintain a healthy BF% under normal hormonal conditions, ie good diet. Your body can shed excess calories in a number of different ways. a) when you eat your body increases it's metabolic rate, how much it increases depends on how much food you eat b) your body will burn excess calories as raw heat c) you experience "restlessness" because your body has extra energy that it wants you to burn d) your body can pass extra food as fecal matter that does not even get absorbed or used in the first place.
If you increased your calorie intake and kept your calorie output exactly the same, then yes you would gain weight. The problem is that the shear act of increasing your caloric intake results in an automatic increase in caloric output whether you want it too or not. This is how someone can increase their intake from 3,000 to 4,000 calories and experience little to no weight gain, if they are eating the right foods.
This is also how hunter gather societies maintained such a healthy BF%. at 15% BF your body can survive for ~30 days without food. There is no evolutionary benefit for going over that BF% because of the diminishing returns you would get from that extra fat storage and the effect it would have on your ability to maneuver and survive in your environment. Plus after 30 days with no food you are pretty much screwed....