I don't believe folks are being dropped if they do not post after six months or so as stated above.
Look at the Members List and on the very first page there is a member from 2004 that has zero posts and he is still listed???? and there are many others on the list with similar stats.
Jeff and the staff of moderators surely have their shoes filled with all the other things that must be attended to so I doubt that they just check the list of members ever so often and deletes those that do not post. Maybe there is some sort of subroutine in the programming that does this for them ... I just do not know.
Many folks come here just to glean information that seems pertinent to them at the time and they do not register. Many do register I guess to mark the fact that they came here in the first place. Many of us came here and stayed because we like the company of the other members.
I personally have many folks from here that I e-mail to on a regular basis and share ideas and thoughts with on the various situations that this Forum does not discuss nor allow. That's fine and I respect that philosophy ... of course sometimes I do throw out some political jabs and get called to the office on them by the mods.
Check out my signature line for an example ...