I have to agree that the 5 posts isn't an issue. Hell this counts as one of mine. The bigger issue (and one that I don't have a problem with) is the four hours.
I guess it makes sure you've at least done a bit of reading and so you should know what the general attitude/mood is like on the forums.
Either that or you just rigged your browser to refresh every once in a while and went to bed
Both are barriers to entry though, which I guess is the point.