Chris jM:

Truly excellent and thoughtful post.

Gute:

Assess anything from Sparks with caution. He's wedded to the M113 as the epitome of mil tech.

With reference to terrain, as ganulv illustrates, 10%, even if accurate is relative. I doubt that figure is accurate and it's in any event totally immaterial. Terrain is but one item in the METT-TC dictum and that dictum should always be assessed in totality and applied to forces to be committed.

You do not fight terrain, you fight people. There are over 400 cities in or on accessible terrain worldwide that have over a million people; in 2008, roughly half the world population was classified as urban. One can use heavy forces in cities but there's a cost and Light or regular Infantry is better suited. That doesn't even address jungle, the Taiga or Mountains where vehicles can go but are sometimes tactically disadvantageous.

There's a place and use for all and too many wars have proven that "One size fits all" is not a good solution. A parochial approach similar to the one espoused by Sparks and too many others as well as the equally bad 'universalist' approach is unwise.