Sorry if this is a dumb question, but why are wings and horizontal stabilizers elevated on posts? If they were glued flat onto the motorstick/tailboom, would that be okay?
First of all, it's not a dumb question! Asking is part of science after all.
So in an oversimplification: To answer your question, it's to adjust what is known as the angle of incidence. if you look at your plane from the side, you will see that the wins/stabilizers will make an angle with the motorstick. You can adjust that angle by adjusting your posts. If you glued your wings and stabs directly to the motorsick/tailboom, you wouldn't be able to adjust the angle. And the angle of incidence is a considerable factor in determining whether your airplane flies smoothly or not.
Also, just a practical pointer, it's easier to store and transport planes if your main wings are detachable from your motorstick. It's hard to do that if it were glued; you'd need a big box