not always true.. i know that I dont like dyno tunes, cos it doesnt really represent what your car is doing on the street.
When I was up in qld, I used gavin woods down in labrador (he is the best ). He tuned it just like that, and 12,000kms later I had it on a dyno in Melb, and they were all asking me where I got it tuned as it was perfect... and after 12,000kms too!