I'm not that familiar with the samples, but they're probably just implementing "linear" tesselation, where more triangles are added, but they don't curve at all to better match the curved surface that's roughly defined by their 'source' triangles. This is useful when you need extra vertices for something like displacement mapping, but not for smoothing out edges.
Catmull-Clark subD surfaces add curvature to the generated "sub triangles", e.g. on the Wikipedia page, you can see a cube bulge out into a sphere. The artist has control over how/where this "bulging" will occur.
Also, these surfaces and their behaviours are programmed into many 3D modelling packages, so if you implement them in the exact same way, then an artist working with Max/Maya/Blender/Softimage/etc can tweak their "bulge"/"smooth" parameters to get the kind of shape that they want, and then know it's actually going to appear that way in the engine too.