You're right that there is a correlation. However, it's important to note that the community is not selecting for identifiable users by not upvoting pseudonymous users. The individuals with the highest karma are typically ones who have earned distinction in their field and are advertising themselves as such. This somewhat identifies them as authorities on certain subjects and their expertise is respected. The system is neither incentivising identified users, not punishing anonymous users. It's just rewarding certain identified ones.