I can see WW point...cause if you are already throwing a bug that's in season and the fish are already tuned onto it, are you really forcing an untimely response from the fish to deviate from its normal behavior? If its taking a bunch of cast for the fish to take a fly that is already in season, seems to me it could be more about getting the presentation right.
In the park, I think the fish are a bit more opportunistic and would eat most buggy looking flies if presented right, year around, hatch or not. I don't know if its forcing a hatch for them as much as its - "hey it looks food and acts like food, might be food-get it before its gone" I think that's why general/generic patterns and attractor patterns works so well.
Regardless, to me one of the beautiful facets of fly fishing is the ability to make it your own. And as such - to each his own.
May you find a rise in every puddle... - WATERBORN