I agree with the above post. C02 is not necessary. Just make sure you adjust your lights and other parameters and select plants accordingly.
I think most people really actually want the low maintenance of a low-light, slow-growth, non-c02 injected tank. The pics of high-tech tanks are just too tantalizing I guess. People on this forum are addicted to c02 injection, and it's not necessary.
No one said CO2 is necessary for every tank. If you insist on running high light, though, CO2 is necessary unless you have a thing for algae.
I love my low tech, no water change low light tank. I also really enjoy my high tech tank. Different strokes!