At full throttle the needle circuit is effectively nullified, since the needle itself isn't restricting anything at all.
The needle circuit limits the flow of fuel going through the main jet, and when it stops limiting it, the main jet orifice size is responsible for metering the fuel.
If the needle jet is limiting the main jet circuit at full throttle, something isn't set up correctly.

Other carbs (non TM flat slides and the like) use different methods to do basically the same thing, so your ideas might in fact be the case with them...I really couldn't tell you for sure.
The TMX38 uses a needle for pretty much all of the circuits, the Lectron uses a needle for several circuits, so changing needle jets and needles have a big impact on full throttle operation.