Keep in mind, OFL's information are more general guidelines as to when you should change your water. Personally, I think her recommendations are just slightly overkill, and arguably stressful for the fish. She also doesn't factor in how many fish you might have in the tank... which, as you might imagine, can greatly affect how often you should change the water.
As a general rule of thumb, not knowing anything about the water, or conditions, her suggestions are appropriate. However, if you can obtain a liquid test kit (API is a popular one), you'll get a better understanding of your particular tank. You might find that you only need to change the water once a week, or you might find that you need to change it every few days. But after a couple weeks, you'll get a feel for what your particular tank needs.
I'm not discrediting OFL here, I'm just saying that some people take what she says as gospel, when in reality, her suggestions are more conservative guidelines.