lol, this thread gave me a laugh.
Of course you aren't expected to read the entirety of a 300 page year and a half old thread just to post in it - it's good if you want to know the skinny on all the ins and outs of an ecosystem like the Stickam regulars or a club/crew you plan on joining - but you can usually pick up the conversation over the last couple of pages to be up to date on current happenings.
It's in the rules because some people just can't get it in their head that this is a community and a discussions board and as such you should at the very least try to contribute to the discussions going on - which means you should be up to date with what is being discussed at the time you post a reply. Threads under 5 or so pages is a no brainer - just read it. If it's over 10 pages and its a serious discussion, a skim of the opening post/first page and the last few pages will probably catch you up - no need worrying about dead ends.
The problem of people not reading things is painfully obvious when they reply on a thread title and it's obvious they didn't bother reading the opening post or any of the replies before writing their own. I can think of a handful of users who have gotten themselves multiple bans for that kind of behavior all in the name of post count. Sort of like the retards who vote on under judgment flash without actually viewing/playing it just for the b/p points.