Not to be the voice of reason here... but all I think Imprezer was trying to say was that a car no matter how perfectly tuned on the dyno will always see some other 'conditions' that you just can't account for while tuning on the dyno.
I agree with you 100% that you can tune the car perfectly... for near perfect conditions. But what about tuning for temp, weather, grad (determining starting/lugging engine load), testing the car down to stall speeds then seeing how it will react to it. Will the fuel delivery be able to react quick enough so that the car won't stall in traffic or sudden on/off gas inputs? These are the sort of things you cannot tune for on the dyno. You can try to get as close as possible and nearly tune the engine, but there is always some amount of variable you just can't figure in until you drive the car on a daily basis.
Now if this is a track car and it will never be daily driven... then I agree totally... you can tune it perfectly with just a dyno. But I believe this, like my car with a TEC-II + Turbo, is a daily driver.
Just my .05 cents, cause I've been there... and I've done that. (Oh... so has Imprezer, but he did it the hard way and I really value his input because of it)