The 7 Rem Mag is here to stay. A good choice for anything in North America with the exception of the great bears and will do fine for alot of plains animals on the Dark Continent.
Maybe that particular store doesn't sell to many but I can assure you they still sell well and you'd be hard pressed going to any hunting camp in season and not seeing a 7 or two being use weather for deer or elk. You want to talk calibers that might not be around in a few years down the road are the Ultra offerings along with the 204. Remington introduced the 5mm Mag in the early 70's and manufactured and sold 60,000 guns and stopped producing ammo. IMHO the round was equal if not better than the current 17 but fell by the wayside.