yeah but the weights used will really suffer. To retain the most mass possible, this is why most guys look like shit when they diet down. They go too low in cals, then stop doing what got them results in the first place. Going heavy!
You are absolutely right. For mass building one must employ lower reps while using ever greater resistance as well as changing up the routine often enough to keep your muscles stimulated. However, if one is carrying around too much of a layer of fat over their muscles, they will simply look fat and not defined and muscular.
As for diet, we all have different metabolisms and our metabolism changes during our lifetime. People with "fast" metabolisms are usually not as fat as people with slow metabolisms. If one is looking to lose weight, they must burn more calories then they ingest. If one is looking to lose fat but maintain their weight they must develop more muscle tissue preferably through exercise such as weight training. On the plus side, muscle weighs more than fat I've been told, so muscular folks can get away with weighing more than not so muscular folks.
I've not worked out for several months. I have dropped about 20 lbs because I am also eating less than I do when I hit the gym on a regular basis. Never-the-less, I believe that I look somewhat fatter then I did when I was working out. Also, my clothes still fit about the same. This is my incentive to get back into it as soon as possible after my impending surgery.