In layman's terms...
They grind the split duration to make the numbers attractive then put a big center line on it like 112 or 114 to take away all the cylinder pressure....it's a scheme dreamed up by the marketing departments so they can sell you a cam that's too big for your combination and it'll still run decent.
True power is built from square cams like 530/530 lift at 242/242 duration at .050 and to increase scavenge balance between the intake and exhaust you use a combo rocker arm system like a 1.72 intake ratio and a 1.6 exhaust.
Here's a good tech article that reallly explains the truth about cams and why they make power...Compliments of the now retired Harvey Crane:
http://www.4secondsflat.com/Cam_Design.html
After reading this you'll realize that all the glossy pages and fancy catalogs are really just a bunch of hocus pocus, real cams are selected and ground by small obscure cam companies like Racer Brown and have been for over 50 years.