ORIGINAL: friz
Wouldn't it make more sense to put a micro servo right next to the engine and actuate the throttle with a little push rod.
It certainly would if the environment around an engine was a bit nicer.
Most servos are surprisingly hot fuel proof. But some aren't. And the vibration around the engine and firewall is quite different than the vibration felt through a servo cutout back in the fuselage.
So most designs consider the best location for the majority of modelers and take the safest way out. Just like they do when suggesting the CG location.