An octagonal gate might have equalized throw, but the engage isn't equal.
http://www.slagcoin.com/joystick/restrictors.html
lol, totally playin' theory stick fighter here. I'm sorry, I'm sorry.
anyway, I would think that if you're riding the gate (which you would probably have to do with an octagonal gate) that introduces tension, and tension reduces speed, which is what I thought was part of the equation (you want accuracy, but you wanna be able to do things fast as well).
supposedly on a square gate, you can hit a diagonal without riding the gate (hence extra throw), which makes more sense factoring in quick qcf motions or stuff like, I dunno, wavedashing, etc.
Like I said, I honestly don't know (waiting for that TE stick, ha) but it sounds like it makes sense to me. I'm biased by that page though. >_>
Um, supposedly the Japanese cabs come standard square, so you could just transfer right over to the arcade machine, but honestly I can't tell you if I'd be going to Japan anytime soon... so I guess that really isn't an argument.