That is incorrect.
It is actually applied to any bare part of the body that could be considered "hot" so as to accentuate it, with a few exceptions. Shoulder, knees, buttocks, as well as the superior portion of the bust is commonly subject to this rule, assuming it is a) exposed/bare b) big. Though usually you'll only see ecchi doing this shit, refer to Horizon in the Middle of Nowhere (or anything animated by Sunrise, really) or Oniai for that kind of thing, though I recommend the former if you're actually going to watch anything at all. I'd post pics but you probably already know what I'm referring to.
The exceptions would be the cheeks (although I guess that could be kinda moe) and the fingers. Why they redden fingers I do not know. Maybe it helps attract attention to the hand, or all those characters have a really high concentration of iron in their blood.