It is not uncommon to glass up a nice Coues buck at 600-1,000 yards across a canyon, bedded comfortably in the shade of an oak or a juniper. Personally, neither I nor anyone I have hunted with, have ever unlimbered the tripod (preferably mounted with "the Claw") or got prone with the rifle over a day pack and proceeded to blast away at the distant animal.
What you do is plan the best stalk that you can and proceed. If you have a companion or companions, they stay and watch the animal, so that if it moves before you get over there, you at least know which way it went. Often as not, some of these stalks end up with the deer having disappeared before you get there. In the latter circumstance, about half the time, the observer(s) don't even see the deer move out--he just won't be there when you get there. That's why they call them the "grey ghosts" and why it's called "hunting", not "shooting".
An outfitter that tells you to be prepared for 600-750 yard shots is more interested in being able to say something like, "Ninety-five percent of our hunters get shots--if you can shoot we can put you on a trophy".
