Originally Posted by merlinextraligh
It's an adaptation to cope with the bike having too much drop from the seat to the bars. It makes the postion on the hoods higher. So you can look OCP with a flat stem and a big drop, but not have to bend over so far, at least on the hoods.
I'll disagree with that just a bit. I have ITM Millenium bars on my bike. I have them slightly angled up to generate a flat portion running from the curve to hoods before the drops drop. In one sense you're correct, this does raise the hoods a bit, but what really matters (for me) is getting that flat portion. Otherwise, my wrists angle forward in this position.
Some bars appear to have the tops, curve and run out to the drops much more on one plane than the ITMs. (I think the Easton EC90s are like that, but I'd prefer to get aluminum if anyone has a recommendation.)
And looking OCP is just a big bonus.
edit - Campy seems to generate a more substantial horizontal space behind the hoods. I wouldn't be surprised if Shimano riders are more prone angling the bars up.