anybody have a good rationale for why handlebars tend to curve inwards (towards the rider)? Granted I haven't ridden that many bikes w/ different bar setups, but it just seems that a flat bar would give better leverage for steering input as well as more comfort w/ hanging off the bike (not needing to crank the inside wrist into ulnar deviation).

It's probably so you don't have to stretch as far when seated.

It's just ergonomics. If you hold out your arms ahead of you then the natural line your knuckles take is not straight - bars are normally made to follow the natural line your body takes. Flat bars will have the slight tendency to make your elbows stick out. I know when I've put absolutely straight bars on bikes they do feel a bit strange at first - you get used to anything of course.

sure! but with ergonomics being so closely tied to performance and control, wouldn't it make sense to have the bars set up in a way that makes a rider more comfortable during their most frequented activity, say, leaning/turning? Obviously some bikes, bars and ergos favor more comfort during straight-line riding in an upright posture.

Just looking at pics of folks on track (not just on SD's), it seems like many have some awkward wrist positioning associated with bar angle, which I would think would negatively impact endurance and control.

I found that the stock bars have to much pull back, sore wrists. I put a full dirt,(read straight), bar on and it was too straight for the reach over the tank, awkward slow speed tight turning. Compromised with http://www.ktmtwins.com/renthal-rc-high-bend-fatbars. Lost the risers with these bars as they were no longer needed. I tend to ride the bike like a dirt-bike though so...

I find the stock bar absolutely splendid. I will agree that at full tilt, full lean forward, I may be bent wristed but overall the ergos are right. Especially for wheelies. I even fitted a pair to my Strom and now it is ready to race too.