I suppose there will always be a degree of commercial consideration but I think the Editors do in fact get a pretty free hand. We all have our own particular areas of interest and I am personally very much in Jim's camp but "Model Boating" is a pretty wide term and if there is good support for hydros and the competitive side then they deserve to have space as well. I know Paul Freshney is hoping to have more coverage of model yachting in future.
The other key factor, as Paul has said to me, is that if people don't write it, he can't print it and there is more than one branch of the hobby where contributors are very thin on the ground at the moment.
Unless you are in a specialist category such as Model Shipwright, every issue is going to contain a mix of articles, some of which will be of little interest to you. It's no different with your daily newspaper or the TV schedules really!