The Scout Rifle seems to be miles away from being a GP battle rifle.
A scout, historically, is a ways ahead of the main group (distance-wise). He's on his own for the moment, and he's covering a lot of ground. Like everybody who carries a rifle around for long periods, a lighter weapon is better. Since any scout worth his salt won't be charging in to unfamiliar terrain like Rambo, he's more likely to be spotting his targets/enemies from a distance. A bolt-action rifle will do for distance shooting just fine. So will a semi or lever - but a bolt-action has fewer moving parts, thus less parts to break. A toothbrush, a boresnake, and CLP should be all you need to clean a bolt rifle.
Stripper clips are a very nice way of keeping ammo together. They're also very cheap and fairly tough. Carrying ammo in stripper clips instead of magazines allows lighter weight and still fewer chances of problems - bad springs in one magazine, having one mag smashed up...
A scout was often all alone for a long period, and travelled light and fast. He wasn't supposed to run out there stirring up the enemy.
The forward-mount scope, from what other folks have said, is good for fast shooting as circumstances dictate.
The Scout Rifle is not a tricked-out battle rifle. It is a minimalist rifle. It is chambered in a medium-power rifle round (.308 or similar). It is usually seen in slow-ROF weapons, due to weight concerns. It offers a great deal of simplicity, reliability, and light weight. It doesn't have a match-grade barrel, glass-bedded stock, suppressor, bayonet lug... it is, again, a minimalist rifle that can be used for hunting or anti-personnel duties.
The AR-15 is probably the opposite. Highly modular, allows high capacity, caliber changes for many ranges and tasks, highly-accurate uppers, semi-automatic fire, a plethora of optics attachment points for scopes, lasers, lights... it's a GP battle rifle (with somewhat shorter range).
If you have to carry a rifle with you for three months straight, with no resupply, which one would you rather have? I think that was what Cooper had in mind - a situation involving long-term carry with very little shooting, in a package minimizing weight and emphasizing simplicity, while providing moderate range and power.