What about the safety aspect? What if there's a fire? Wouldn't it spread much faster to these wooden buildings..then concrete?
How about areas with winter climates? I don't think they would be able to retain heat as well.
AFAIK wood can be made relatively fire-resistant via lamination & treatment. Plywood and Concrete can have similar r-values (depending on lots of variables). You get most your insulation from... insulation. I saw a wooden house with R60 once.