No matter how good your writing is, if you don't have a full time sales guy selling ad inventory, you aren't making a living. And therefore, the more writers you have - the more inventory you have - the easier it is to sell the inventory. The more inventory you have - the more money you make - the more sales people you can hire. And the cycle continues. Pretty simple formula.
So, if you are blogging for profit and you aren't playing on a team or teams or atleast have a sales team working for you, you won't be blogging for profit very long.
If you want on my team, give me a call.
(SideNote: this is also why google's API is exciting. Developers now have access to unlimited inventory. How long before a smart sales guy with a development team realizes this, though?)