Lots of guns will kill elk. The "eastern view" you refer to is probably a combination of magazine articles and wanting an excuse to buy a "western gun."
As others have pointed out, lots of westerners carry magnums as well. Part of it is ignorance, part of it is necessity.
I live in the west and carry a bunch of different elk rifles. Some days, in some places, I want my .300 WBY. Other days, I'll happily pack my .260. Just depends on the menu.
Magnums aren't necessary, but they are nice to have once in a while.
