Binko, I think you've pretty much nailed it.
Sure, "masa" means dough, and even more basically it means "lump." Then again, pasta means paste and mostaccioli means mustaches.
In the Mexican vernacular, it is my understanding that masa harina refers to the dry, powdered stuff, while masa means fresh masa, i.e., the stuff that we are lucky to have that most other places don't. I do not think that the Chicago beef stand tamal usually is made with masa harina, which I doubt is widely available where it arose. Corn meal, perhaps, as the texture is somewhat like bad polenta (in a good way). So, let me backtrack a little from what I said above about "most" US tamales being like the hot dog stand variety. At this point in US immigation history, "most" tamales are probably "more" Mexican and likely made with masa harina, which is bagged and sold in even the weakest Mexican bodega (but not fresh masa). I'm sure someone in Mexico eats masa harina tamales and tortillas, just like someone in France eats Wonder Bread and Hostess cakes, but it is not what I associate with the culture. In the areas of new immigration here, however, it seems folks generally make do with the bagged stuff.
The tamale trail site I mentioned above has a recipe that calls for either corn meal or masa harina, so until I get down to Doe's, I'll have to guess what is in their secret recipe.
http://www.tamaletrail.com/recipe_howto.shtml
Bayless explains masa very nicely on the Frontera site.
http://www.fronterakitchens.com/cooking ... _masa.html