The thread pitch is taken into account in the nominal diameter of the bolt("D" in the calculation). A smaller bolt will have a smaller thread pitch and therefore a greater mechanical advantage, so when you multiply by .5 for a 1/2" bolt compared to .75 for a 3/4" bolt you are accounting for the difference in thread pitch. As to fine vs. coarse thread, because a fine thread bolt has shallower threads, it has a larger cross-section that needs to be stretched to achieve the proper bolt tension so it requires higher torque to do it. The constant K=1.33 in the calculations above is something Rock Crawler uses, but is not included in any other equations I've seen to find bolt torque, so they are increasing torque significantly and I'm not sure why. The coefficient of friction should account for any variation in conditions that would affect final bolt tension.