I don't have any problem with the method. About the only time I've concerned myself with this type of calculation is when I want to use a hop that has an alpha number a lot different from the recommended hop. If they call for 12 units and my hop is 11.5%, I toss in an ounce. If my bittering hop is only 7%, I'd use 1 3/4 oz.
Some people want to know exactly what they put in and even go so far as to include the aroma and flavor hops in their bittering calculations. Considering they have no good value for their utilization, I find this compulsiveness amusing.
Measure with a micrometer, mark it with chalk, and cut with an axe.