The thing is, you never want
all your members to post regularly.
X10 has over 100,000 members right? even if they each only made 1 post every week, thats still an average of 15,000 posts a day.
Do you, I or any of the moderators really want to wade through all of that to find the useful / funny / informative posts?
Even if the average post quality remained the same (which in all likeliness it wouldn't), you'd still have a proportional increase in rubbish, pointless or offensive posts.
With the increase in traffic, without a substantial increase in moderator strength, many of these "bad" posts would simply get absorbed into the ether of "ok to moderately poor" posts and get generally ignored.
If sheer member count is a intimidating, what about the post weight? On the largest, fastest moving forums I've seen, newly posted topics from users asking legitimate questions often drop off the first page in a matter of seconds. Thats a sucky experience for the person just looking for some help.
When there is a particular big-ticket news item popping up relating to a particular forum, you often get 5 or 6 people posting about the same thing, wanting to be "first" rather than waiting and doing a search for posts on the topic. Not only a moderating nightmare, but it creates a completely fragmented discussion on a given topic.
Then there are other issues, if you send out reminder emails, people will only come on and post "I got an email that told me to post so thats what i'm doing." Would you really want that? More spam, just so your forum is more 'active'? I certainly wouldn't. People should be posting because they want to, not because they have to.
Signing in once every two weeks is relatively painless, and it gets at least 1 ad view, 3 if they haven't got a cookie.
Besides, the internet is all way to full of recent-ism anyway. So what if one dude hasn't posted in 4 years? He may want to come back eventually, deleting his hosting account is fair game, that takes up lots of space and (potentially) bandwidth. Forum accounts a cheap; just a few entries in a table. If you really want to save space, cull the old posts. Deleting his account without telling him would be very rude.
My general point, I guess, is that you
want the majority of your members to be lurkers. Sitting back, reading the posts (viewing the ads), with a minimum of server load and moderator work. Then occasionally popping out of the woodwork to make a
good post, on something they actually have an interest in.
You don't want people to post for the sake of posting, or worse,
EVERYONE posting because they
WANT to post
ALL the time; that would be absolute chaos.
(did i meet the 'no one-liners' requirement?
)