I think that exploration in ED is a special case. Because, in a "social" game like ED, exploration is rather anti-social by design. So it's quite understandable, in order to break the anti-social monotony, or to have any social aspect to exploration at all (like showing off the weird things you might find to other people), that explorers are much more likely to go to the forums and/or use third party tools.
The ED:EDSM ratio of about 3:1 is what I would expect.
For just travelling around the bubble, the ratio between "hyperspace jumps" and "hyperspace jumps logged by third-party tools" is around 20:1 [1]
Out in Colonia, it's around 6:1 - more explorers, more experienced players - but still the substantial majority of activity is not logged (and Colonia itself, which is the system most visited by people passing through rather than resident, has a ratio more like 8:1 or 9:1 ... so that might be a reasonable proxy for "explorers")
For a "visited stars" ratio of course it helps that a system only needs to be logged once regardless of how many unlogged visits it has, which is especially beneficial for the more heavily explored areas. Nevertheless, I'm quite surprised about 3:1 (or as marx says, closer to 2:1 for recent exploration) based on the above ratios - it's still surprisingly good.
[1] And since it's likely that the players using third-party tools are more active on average than the ones who don't, the ratio of
active players is likely even wider than 20:1
