Actually, I don;t believe that the same logic applies simply because you can use the same bullets in each.
In the -06, since it was developed originally to be used with a less efficient powder taking up more case capacity, you are limited to a max pressure of 50,000 CUP. With the advent of modern powder, the 308W can handle the same powders (and a little more, max pressure 52,000 CUP) to get equal, or in some cases, better velocity with equal or less powder. In the case of the 300WM, you are using significantly more powder and are going to require the case capacity to accept that increase. The same is true again when you move up to the 300RUM.
The difference is that despite the case capacity, you can't safely charge an -06 case to 300WM levels, but you can charge a 308W to match (or beat) an -06.
Now, I am definitely not promoting the 308over the -06, or vice versa. But I love my collection of 30-06 rifles and one pistol. The only 308W that I have is a barrel for my Encore, but I hunt 90% of the time with the good old -06.