RE: 30-06 jack of all trades master of none?
The salesman is trying to make a sale: that is his job. Of course, he should be informed about his product, but this isn't required in many cases to sell. Imagine a woman's response to this who is buying her husband a rifle on the basis of knowing that he has been lusting after a .338 Win Mag for Elk hunting but isn't herself knowledgeable about guns. She would have gone home with the .338 Ultra Mag I suppose.
In all probability you know substantially more than the salesman about rifles and cartridges. To suggest the .338 Win Mag is a minimum for Elk is to be very ill informed about that cartridge. And it isn't like this is an obscure cartridge. It is a very popular cartridge, and a lot of rounds of ammo for it are sold annually. He just flunked Cartridges 101 I guess.
Or, as Charlie Brown suggests, the world is evolving. Smokeless powder is becoming less potent. Lead is becoming less dense. 0.338" diameter is shrinking.