When you comparing Chemical Fertilizer with Organic it is like comparing apples with oranges. With Chemicals you have to worry about loosing the nitrogen due to evaporation if it does not rain in a few days. Or loss of some of the NPK do to run off or leaching if it rains too much. With organic or in this case chicken litter, you dont have the run off or leaching problems as much, and you dont have to worry about evaporation.
When you look at a chemical fertilizer and see 17-17-17 that is the total numbers of chemicals. Then look at Organics and see 3-3-2 that to is the total number of organics nutrients in the product you are putting out but those numbers are what is actually fed to the plant. But then again look at the soil building abilities of organics compared to chemicals. So I believe that is it not fair to compare one with the other just looking at the numbers.
You are right about the litter lasting longer, the only thing I would worry about with litter is where does it come from? I have a customer that used Chicken Litter from his neighbors chicken houses for years until they changed the feeding program for their chickens and he said that "baby chicks where taken into the houses and less then 2 months later full grown chickens were coming out." What ever they were feeding those chickens he didnt want it on his property or in his water well. Now I do have customers that not only put Micro Organizims on top of the litter from there own chicken houses but also spray the Organizims in the houses to detoxify them and keep the smell down. The Micro Organizims decompose the organic matter and feed it to the roots of the plant.