For online retailers, the 16th is the SHIP date, NOT the arrival date. Unless the retailer has an agreement with Sony (Amazon might), they CANNOT ship the product prior to the street date. Street dates are a very touchy subject with Sony (among other companies), and violating the street date (including dropping the product into the transportation system) is a serious offense and can result in the retailer losing its license to sell products from said company, as well as large fines.
Since Amazon and Gamestop are both still considering GoWIII a preorder item today tells me that neither company will be shipping it until tomorrow. Normally if Sony has released at least Gamestop to ship early for arrival on the street date, the tag on the Gamestop page changes from "Preorder ships..." to "Now Shipping" the day before the street date. As of 4:00pm EDT, the Gamestop tag still states "Preorder ships 3/16/2010."
I always order games from Amazon and as long as you pick release date delivery or overnight for shipping I've always got the games the day they are released. I recieved an email today from Amazon informing me My God Of War 3 Ultimate Edition has shipped and will be at my house tomorrow.
That doesn't apply to all online retailers. Best Buy has this option called Street Week Choice where certain games will arrive at your home on the exact release date of the game. I got my confirmation e-mail this afternoon and GoW III will be here tomorrow.