Linux' structure is compeletelly modular, one can have an operating system with only the software that is necessary for it's purpose. At the same time, it is perfectly possible to install dozens of GB of free software that is available, including graphic environments, in any linux system. The same thing applies to all unix-like operating systems.
So it is actually up to the administrator to make responsible choises about what we wishes to install, following the golden rule that the less installed things the better.
