The point is, if it weren't for disney et al, SMB would be public domain in the next couple of months.
Super Mario is not something that has always existed or would eventually exist, it is a creative work that became successful through Nintendo's efforts. There is nothing wrong with Nintendo wanting to reserve their rights to it.
That is not to say that Mario fan works are not enjoyable - there are awesome Mario ROM hacks and Flash animations out there - but that people shouldn't feel entitled to the rights to make them and to complain when Nintendo takes legal action.
Nintendo is reaching disney-level reliance on their cartoon hero, (probably worse) so I wouldn't be surprised to see them becoming another copyright-extending villain over the coming decades as they struggle to survive with their seeming lack of creativity.