Since when??
I know for sure that neither SF4 nor Marvel3 ban this?
Full Schedule had WIRED two buttons to be multiple DIRECTIONS (upback, upforward) at the same time, and it was allowed at some tournaments (UFGTX!).
People in SF4 either use eg PPP macros -- or worse, use the 8 buttons to have a 2nd LP and a rewired Select on their Stick, to get access to easier Back-plinking.
To quote the rulings from the (by your opinion) "best-run tournament ever"
http://ufgtus.wordpress.com/2014/03/16/hardware-button-bind-ruling-for-ufgt10/
"Hardware Button Binds, so long as they trigger all of their inputs on the same frame, will be allowed at UFGT10 and any of my future events. These Button Binds must be either directions only, or action buttons only."
Clearly allowing a Button that presses LMH at once -
And this is talking about REWIRING the stick to do things OTHERWISE NOT POSSIBLE IN THE GAME; an entirely different case from "Going to the Button Configuration and binding your buttons"
And obviously neither a hardware macro like that, nor doing something that is explicitly allowed by the game itself (Button Config!!) is in any way, shape, or form comparable whatsoever to Turbo - which is
1) Not part of the game itself
2) Multiple automated button presses, one or multiple frames apart
3) Allowing things which are humanly impossible (I can't press depress press depress the same button 30 times per second)
Turbo is more akin to programming a "macro combo", where I hit a button and then my Stick runs through an entire combo; that has literally nothing to do with the question at hand.
I have no idea how someone who wants to avoid Half Circles, laughs at games requiring 3 Buttons for Supers, hates execution this, hates execution that, gives leniency on every input, etc whatever.. suddenly thinks it's reasonable to expect everyone to be able to press diagonal buttons on the same frame (and it is crucial to get this right every time; If you do it wrong, your "Downback+Updocall vs a Low" turns from 'landing a combo on your opponent' into 'getting happy birthday'd'; about the hardest possible swing between "Got input right" and "Got input wrong" you can even have in the game) -
And it's not like this is for some "special technique" which beginners have no access to (PBGC, Wavedash, Similar - those aren't easy, but they're also clearly advanced mechanics, which you don't even attempt until you are experienced), but for literally the most basic thing one can do in this game sans moving the stick / using one of the 6 attack buttons.
5 Frame input delay on Macrobuttons on Stick sounds like the most convoluted arbitrary execution barrier anyone could even dream up. Are you trying to get hired by Capcom?