If anyone in the world cannot wait 2 miniutes then we have a impatient world, simple as that!
But really, 2 miniutes is not that long to wait. Given the amount of users here as well, it's reasonable plus the server doesn't have such a hard time handeling all post requests as it would have with a very low time limit between posts.
Also, it would promote people going on posting sprees. If I could make a post every 10 seconds, in 2 miniutes I would have 12 posts, and I think the server would crash taking that many requests at once if we say had about 15+ users all posting every ten seconds (12x15 = 180, meaning 180 posts total in that time frame of 2 miniutes, and the server would come under a lot of load and could crash). Not also to mention, I don't think everyone would read all 180 posts/replies made by that amount of users, considering trhe short time frame that amount of posts was made in. Not to mention, I could spend 10mins on the forums, if a ten second post limit was in place and make60 posts in that time frame.
I guess I took out the trouble of doing the Math for some people =P.