Not at all. When light is passed through a small aperture it can interfere with other light near it. That's a real simple explanation of the physics of it. What that means to a photographer is that if you stop down your lens too much you will start to lose resolution instead of gaining it.
You normally gain resolution when you stop down a lens because there is less tendency for aberrations in the glass to show up. You have to remember that you are bending light in order for a lens to work and different wavelengths get bent different amounts when they pass through glass (think of a prism) and lens coatings try to correct for this but there are practical limits to how perfect you can make a glass surface and how well these coatings can work in the relatively cheap lenses photographers work with. These are consumer lenses and they have price constraints.
When you take smaller samples of the light by using a smaller aperture you tend to have less problems therefore increasing your resolution when you stop down the lens. However, at some point you will start getting destructive and constructive interference when all the light hitting the sensor is coming through a smaller and smaller holes. If it was simply destructive interference then you would start losing your reds starting at deep red and going through the spectrum until you hit deep purple. Light waves can combine to make brighter, constructive interference or darker, destructive interference so instead you just start to get fuzzy reds then oranges then yellows etc... as you stop down a lens. As you decrease the aperture, higher megapixel cameras will start to pick up on this fuzziness and lose resolution.
You are never going to get better resolution with less megapixels in theory (of course there's a lot more problems in real life with high megapixels e.g. increased sensor noise and other stuff I'm not going to discuss right now). What all this technical crap means is that if your goal is to get as much information into your landscape photo as humanly possible, really small apertures are not necessarily a good way to do it. You may gain DOF but you may lose detail. Ultimately there is a sweet spot in each lens that will give you the most possible resolution where you get rid of enough lens aberration that decrease sharpness without losing too much to diffraction. Higher megapixels cameras on really nice glass tend have a smaller sweet spot because it will pick up the diffraction problems sooner.
In practice you want lots of megapixels as long as the pixels are of a good quality for landscape photography so you can pick up fine detail. There is a tipping point however where you are just not going to get better resolution with more megapixels and we've hit that point with the D800 and even some of the really nice glass. However you have to make a decision as to what aperture to use based on the DOF you need and how your lens performs as far as aberrations are concerned and also depending on how much resolution your sensor can get. You will only figure it out by taking lots of pictures and paying close attention to your results (have fun pixel peeping). Basically this article is saying that you don't want to just set your camera to iso 100, F22 or F32 and sit there for half an hour for the exposure. You will lose a lot of detail from diffraction. Just test out different apertures, ISOs and Fstops til you figure out what gives you the best picture for you combination of camera, glass and subject. Don't worry about the math or this article, just don't be dumb and close down your aperture as much as humanly possible and think you will get a better picture.
If parts of this don't make sense please realize that it 4am and I have insomnia and this is my way I'm getting to sleep tonight. I'd love to hear well intentioned corrections if I have something wrong but take my writing with a grain of salt. I think I understand the basics of this topic but I may not have done a great job explaining it.
On a related note, I have cheap glass and I'm not huge into landscape photography but what do you experienced landscape photographers think about focus stacking for landscapes as a way around the diffraction and DOF issues you can run into in landscape photography? I know that it requires a specific subject (not catching clouds in the perfect formation or sunset pictures) but I've been screwing around with doing HDR focus stacking landscapes mostly as an experiment (lots of fun spending hours in photoshop stitching together thirty photos to make one). Is anyone actually doing that stuff? If so, have you got anything good with it? I've done it a couple times just to see if I can do it and the results are kind of interesting. Anyone else try it and what do you think?
