Part to the issue I think is that most plans show suggested locations for the radio and (obviously) the engine, and that little teeny mark for the CG that the builder probably does not fully understand. This will work well if it is an ARF shipped with the a standard radio and engine combination but may not work if heavier servos, lighter engine, etc are used.

Most R/C flyers are not full scale pilots and have never"felt" the difference bewteen a full forward and a full aft CG location in terms of control pressures required and the general stability of the airplane at both low and high speeds.

And as pointed out above, the normal solution for recovering from a bad R/C flight situation is to add full power - a technique that may work in an over powered R/C model, but not in most full scale aircraft nor in many scale R/C models.

Personally, being a full scale pilot I am a believer in proper CG location and, more importantly, in locating the CG intentionally forward or aft in small amounts to achieve a desired performance goal. A slight change in CG aft can make that previously sluggish model very fun to fly, a little farter aft and it can become aerobatic, too far and it can become uncontrollable.

The location on the plans is a good starting point but if you are serious about flying (full scale or otherwise) you really should understand CG enough to know what it does for stability and performance.

What many modelers also forget or perhaps never knew is that relocating the CG will also require some adjustment of control throws. You really only want enough control throw to make the plane do what you want and no more to avoid a loss of servo resolution and also to make things less twitchy in the middle of what is otherwise a restricted range of usable servo movement.

R/C models do have a very wide CG envlope which is a good thing as most R/C models also carry all their fuel well forward of the CG. A .40 sized 5 pound sport model can get by carrying 10% of it's total weight in fuel well ahead of the LE of the wing, but I know of no full scale aircraft that would be able to accomplish that. It would either never get off the ground due to insufficent elevator or if if got into the air, would eventually become uncontrollable as the fuel burned off and the CG moved past the aft limit. The fact that R/C aircraft can accomplish this still affronts my aviator instincts as an unatural act that should cause the earth to rise up and smite the plane for it's insolence.