seems to me that if it walks like a duck, quacks like a duck, then it must be a duck...

line weights are based on exactly that, line weights. The standards depicted below are from AFTMA and establish standards to determine the correct line weight...'course, that doesnt mean that everyone has to subscribe to that standard, but if a line weights out at 210 then it is an 8 wt according to this standard.

AFTMA Fly Line Standards

Weight Size (grains) Tolerance AFTMA (the former American Fishing Tackle Manufacturers Association- now the ASA- American Sportfishing Association) Fly Line Standards were developed to help fly fishing tackle manufacturers create a system that would match fly line weight to fly rod performance. Cortland Line Company?s Leon Chandler was instrumental in initiating and completing the project. In theory this would standardize fly tackle manufacturing across the industry and enable fly fishers to select and balance their equipment for optimum performance.

The system uses the weight in grains (a very small weight measure) of the first 30 feet of fly line as a standard. The table below shows fly line weight designations and their grain weight. The system also established a tolerance level that is acceptable.

1 60 54-66
2 80 74-86
3 100 94-106
4 120 114-126
5 140 134-146
6 160 152-168
7 185 177-193
8 210 202-218
9 240 230-250
10 280 270-290
11 330 318-342
12 380 368-392

For each weight heavier than 12, add 50 grains to the previous weight.