This is a great subject, I am certain google has a way of limiting traffic. I've created enough new sites over the last couple of years to know this issue is very real. More recently I had a site jumping between #3 & #9 for a 3.5 million per month term. Volumes would vary from 35 vistits per hour to 140 vistits per hour, shortly after we dropped away to a steady #8 - 9 and peaked at 25 - 30 visits per hour. The last couple of days we are steady at #6 and peaking at #40 per hour. My point is this, we are still a long way below the 130 per hour and we have sinced moved into the top 5 for another high volume term on the same site and the traffic level remains about the same. Google is giving with one hand and taking with the other. It's clever, they have so many versions for any given search term it makes their system that much harder to game and they can still return good results. I think at some point you do break through this threshold, once you gain the right amount of points. Content alone will not get you where you want to go, I've tried just adding more good quality content to a couple of sites and the traffic remains about the same.