I actually agree with this, it makes sense to have to browse for a set amount of time but a quota of posts is a bad idea. Pretty much everyone's first 5 posts are spam posts which lowers the quality of the newbie section so greatly. This could deter new users from becoming active and using the site.
I think it's a good idea because it is an indicator of future forum behavior.
If we all agree that the 5 post rule contributes to worse newbie posts, then spam posts definitely don't reveal a user's future forum behavior. I've only browsed here for a couple hours, but I've already seen many posts from people waiting to post their interesting questions to boards outside of newbie jail.