I think that most of the time when people get away without doing regular water changes and without having to cycle, it is because they chose hardy fish that can survive in harsh conditions.
Fish, like every other animal, produce waste - solid as well as liquid. A filter can effectively remove solid waste for the most part, but it does nothing to remove the urine from the water. And who likes to swim around in a tank of their own waste?
Think about it, would you make your cat use a litter box that you only cleaned out once a year? Would you make your dog do his business in his dog house and make him sleep with it? No. It causes health problems and it is inhumane.
The same holds true for your aquarium. Fish are constantly immersed in the conditions they create, but in the wild they have the advantage of hundreds of thousands of gallons of water volume to spread and disperse these wastes so as not to accumulate to dangerous levels. Comparitively, our tanks are miniscule and accumulate waste much faster. That is why they rely on us to periodically remove some of the dank water and replace it with fresh new water.
So you can see why it is so important for us to perform these water changes. Will the fish live if you don't? Sure, the same way your dog would live if he had to walk around in his waste all the time. He just wouldn't be as happy, as heathly, and likely would not live as long.
