Control is part of it, but it's also due to the fact that it is hard to implement features to work in a heterogeneous environment. The temptation is to dev and

Control is part of it, but it's also due to the fact that it is hard to implement features to work in a heterogeneous environment. The temptation is to dev and test a fully deployed environment, when really you should test probable configurations with several pieces either missing or performing badly.