You're right. It is absolutely important to keep weight in mind. For example, even if I were to build a fully sheeted wing from scratch, I'd use Hitec HS225 servos in the wings to run the ailerons. After all, they save you about an ounce each compared to lots of the standard servos.

Everything should be considered all the way down the line. Beginners do need to hear about that "everything", because there are lots of them. They also need to get a perspective on the values of each, what the choices cost, and what they get you.