[dotancohen]

Interesting. I'm also in the top 2%, but I'm far from being an early adopter on that site, with a userId in the hundreds of thousands: https://stackoverflow.com/users/343302/dotancohen

I was never even very active. I can only suppose that only 1 out of every 50 signups ever accrues any real significant amount of rep.

[int_19h]

There's definitely a strong compounding effect over time. I have a 6-digit UID there, but haven't been active for years now. However, I'm still in the top 0.16%, largely thanks to a steady trickle of rep from all those old answers that are still relevant.

But any such "interest" does apply to the magnitude of the initial contribution, so merely being around for long is not enough - you had to have a sufficiently productive period of activity to capitalize on.