Some of the finest two-handed rods made in the US of A are even more versatile - look at Bob Meiser's rods, many of which have THREE weight designations, for example 4/5/6 or 5/6/7.

I agree with the sentiment that this system can be applied to any rod. Line weight manipulation is effective for various casting scenarios (brookie streams vs. open tailwater) as well as for changing rod action. Personally I LIKE to experiment with lines though this is a matter of preference.