The problem arises because of spammers...many of the features have been locked down, to prevent them from getting any further.
It is more an antispam thing, it attempts to prevent spammers registering for the forum, and editing their profiles to be full of links...if they don't post, then it is hard to keep track of.
For me though the main reason is the blocking of Personal Messages. Since someone needs 20 posts before they can send a PM, spammers cannot register, and start spamming everyone through PM's...
The only problem is that when the do register, they can still post...until they are caught that is...though generally the mods are fairly quick on this.
The issue here is that it may not be easy to selectively block certain things, so it may be all or nothing...
The idea of having this information available easily, would (IMO) lead to users doing what you did and posting things that would be considered spam, just to get post count up.
That thread to get to 20 posts, would be considered spam, and would be deleted as such.