(This question may betray a complete failure to comprehend our caching structure, but...)
This information is taken from data served by the squids... don't logged-in users mostly bypass the squid servers in some way or another, or is that only when actively editing?
As I understand it, they don't technically bypass the squids, but the squids pass their requests straight through to the main servers rather than returning cached pages. The squids should be able to gather stats on logged in users.