A skimmer is a tool, just like refugiums, DSB's, etc. ad nauseum, to assist the hobbyist in sustaining a natural system in an artificial environment. In the 35 years I have been in the hobby, I have seen myraid changes in theories, concepts and practical applications.
Before those who would object chime in, I would still consider refugiums and other "natural" filtrations systems an artificial environment. I do not believe that it will be possible (in my lifetime anyway) to duplicate the miracle that is a coral reef within a container of glass or acrylic.
Having said that, I believe that there are many different ways to have a successful tank. It does not have to include a skimmer, although it is an extremely useful tool that can make many tanks successful. In the end, success takes a lot of study, a significant committment of money and/or effort, and a little bit of luck. The most important thing is to enjoy yourself, otherwise the efforts are wasted.