yes thats true,but the limits of accepted gui conventions were reached years ago (besides to be honest compare mac and pc theaters no reason why close has to be in the opposite corner in a mac its there just for the spite of things). And it actually makes sense, because it makes moving things easier. Becacuse you can use the pointer to aim stuff. Its jsut something you can use to your advantage.
Classic example. make a complex polygon and you want to extrude it about as far as some visible feature. Then what you do is you move your mouse pointer above your firt reference point, you don't need to care about where your tool icon is because it does not come to play then just middle drag the ditance on your nicely zoomed view port and you can do functional measurement whit the mouse. Now the question comes in mind why is it so damn hard in other programs, and why would i like to loose thsi ability.
try this on a 2 button system. select a tangentmove your mouse to reference point, now click and drag the reference to a second point. Well in normal paradigm you loose the ability. Or what if you wanted to move a point and a tangent simultaneously. Its usefull.
PS: middle mouse is used much on unix systems, and nowdays in windows too. Just because its unusual doe not man it does not have merits. (for exaple i never use a scroll wheel to scroll i can accomplish the same with middle mouse but into 2 directions, wich eaves scroll free fro something esle)
Theres lot in normal computer paradigms that suck frankly. fisrtoff why windows, they tend to use space of your screen optimally, what if the system could somehow intelligently dock up all windows depending on the task or atleast share window boders better. Why do we only have 3 or 4 modifer keys and why is there only one menu, and do we need it. Should gestures become norm in the future.
The biggest problem with current paradigm is that its lazy, its for the lowest denominator. Nothing wrong with that IF your actually targeting to be the worst user ever.
But also the simple fact that the normal paradigm isnt meant for 3d, or the kind of complexity we do daily
the bottom line is you can flame it all you want or use it to your advantage ist all up to you really.