RE: Just one engine question. I always wondered why.
Weedeaters have a type of compensating carburetor as well...
The Walbro, or Zama, etc. have a diaphram that acts as a fuel pump and there are passages inside the carb that help to (somewhat ) regulate the fuel flow...
If you have extreme weather changes, the weedwhacker will also run lean or richer than optimal, and a little tweaking of the needles helps.
They're also sensitive to the oil ratio.
A typical glow (AKA "Nitro" ) engine is designed to be easy to operate, and be cost effective to manufacture, and not too overly expensive to purchase by the end user. If they (the manuf. ) were to add a more complicated carb, would you want to spend 50 or 100. (or whatever ) more dollars for it?
The same, typical, 2 stroke glow engine only has 2 needles...very simple actually once you get the hang of it.
With some practice and experience you will be tuning your engine by reflex, or almost automatically...it just takes some time to learn how...