Jason:

I'm glad you're experiencing success -- but if you are "gaining muscle and losing fat as I desire, without any difficulty whatsoever," you are in a small minority. 

"The authors review studies of the long-term outcomes of calorie-restricting diets to assess whether dieting is an effective treatment for obesity.  These studies show that one third to two thirds of dieters regain more weight than they lost on their diets [emphasis mine], and these studies likely underestimate the extent to which dieting is counterproductive because of several methodological problems, all of which bias the studies toward showing successful weight loss maintenance." (Mann 2007)

And again, as you state, "so long as my diet is composed of a reasonable amount of each macronutrient, [...] and a sufficient variety/level of micronutrients, the only other factor that I need to concern myself with is calories."

So we've established that a "calorie" of Coca-Cola is not equal to a "calorie" of wild Alaskan salmon, because one fulfills your macro and micronutrient needs, and one does not.

Unfortunately, macronutrients aren't all equal, either.  As I've proven in subsequent installments, a "calorie" of coconut oil doesn't make you as fat as a "calorie" of butter, and neither makes you as fat as a "calorie" of carbohydrate (Part III); and a "calorie" of protein doesn't equal a "calorie" of anything else (Part IV, Part VI).

Then there is meal form and timing: a "calorie" of food makes you much fatter if you grind it into powder first (Part II); a "calorie" of carbohydrate eaten at breakfast is not equal to a "calorie" of carb eaten at dinner (Part II); intermittent fasting changes the amount of "calories" in food (Part VIII)...

Unless you're weighing everything on a gram scale, your estimates of "calories" are so far off that differences of less than 20-30% will be totally masked by estimation error (Part V).  And we haven't even accounted for the effect of different foods on hunger and satiety (see my series "Why Are We Hungry?")

The one case in which "calorie counting" sort of works is when you're eating basically the same foods, just in greater or lesser quantities.  And even then you'll have to make a very large change in "calories" to see a smaller change in bodyweight over time, in order to overcome measurement error (discussed above) and the fact that the 3500-calorie rule completely fails in all metabolic ward studies (Part II). 

Result: almost all of us will produce better results by focusing on which foods we're eating, when we're eating them, and how they're processed than by focusing on the number of "calories" they contain. 

Yes, if we're absolutely sure our diet is already optimal, we can start counting calories -- but doing that first, as is the current mainstream advice, usually just leaves us hungry and leads to failure.

And yes, one of my future installments will cover the question "So when is a calorie still a calorie?"  There are some substitutions that don't seem to matter, e.g. substituting non-MCT fats for carbs, or vice versa, above ~10-15% carb intake.

JS

Paul:

"if somebody wanted to lose 10 kg, and he/ she did not care whether it came from muscle or fat or any kind of ratio of the two, calories in vs calories out would be entirely appropriate."

That has been conclusively disproven in multiple studies via well-controlled, peer-reviewed science. See the comment directly above yours for the links -- or those in the GIANT BOLD-FACED WARNING at the bottom of the article, both of which you neglected to read.

I'm sorry you're stuck in a long-disproven paradigm: it will make your life, and the lives of those to whom you issue your well-intentioned but utterly mistaken advice, much more difficult.

JS