Memories are vague by now. As I recall, D Fir was the defacto premium lumber for framing etc. But we can't hardly build everything out of a wood that grows in such a specific region. Pine does offer a superior R value for the construction of log homes. The lighter the wood, the higher the R value.
Spruce, pine, and H Fir are also good if properly processed. Especially when considering the strength of southern yellow pine. I think it may be "somewhat resistant" to rot and bugs as well.
If only giant redwoods grew everywhere. I think we shipped a lot of that wood to S America for use as railway track. Especially Chile.
Imagine if cottonwood and poplar was a great building material. Woohoo!
Douglas fir grows all the way into mexico, and into canada, as far east as Montana and Wyoming, including parts of Colorado, Utah, Nevada etc. It technically has the largest natural growth area of any of the major lumber woods. So no, its not hemmed into a specific region.
Its been planted throughout Europe and eastern Canada, for commercial lumber. (though for some damned reason they prefer Sitka Spruce in Europe? I think because it grows a little faster and has much smaller limb structure, so it can be harvested earlier...)
"hemFir" is white fir and Hemlock, milled out of the same pile of junk wood, but still pays better then pine. Then "hemfir" is sold as its own species at hardware stores, because its cheap. ("white fir" being Grand, Noble, Silver, Alpine etc they all get lumped into the same pile with Western Hemlock)
As for R value? I don't think solid wood next to solid wood is going to make all that much of a difference one species to the other, however, pine is not very rot resistant at all, where as Doug Fir is. the R value argument, is null and void when you consider that chinking, windows and other weather protection is where most of the R value is lost in a log cabin (or any style of home really). Don't let the manufactures lie to you on that one, they use pine simply because it grows straight, is easy to work and is cheap, though I'd bet that more use Doug Fir simply for the rot resistance and strength.
Redwood isn't actually a very good structural wood, its very close to cedar and cyprus being rather soft and somewhat brittle, the railroads, ALL OF THEM preferred it because of its natural rot/bug resistance and its very resistant to fire, which is important when you're dealing with coal/wood fired steam engines. It does make a rather excellent wood for siding and decking though, much like cedar. Modern sleepers(cross ties) are going to be red oak or Doug Fir, for strength and rot resistance, notice pine isn't in the equation.
