There's so much done in the modern game market to try to generate as many launch sales as possible. This is due to the way the market gauges success, wherein a game is required to make a certain amount in a specific small time frame to be considered a success. Such has generated the existence of pre-order bonuses, and the more modern "upgrades" to so called special editions.
Saints Row IV is just another game this generation following that path. It's still unknown if an actual special edition is coming (but there was a survey asking about tangible items for it). Either way, anyone who pre-orders the standard game is "upgraded" from a regular purchase to the Commander in Chief edition.
As you might expect, this change which has no extra fee is basically just another way to describe pre-order DLC. It comes with an Uncle Sam outfit, a jet that is painted to look like a bald eagle, and the 'Merica weapon. Really, that gun in particular looks the best with its flamethrowers, "dub step guns", and rocket launching capacity. It's a shame that it apparently won't be a part of the game proper.
Saints Row IV is set for launch August 20th for PS3, 360, and PC. It will also be the first Saints Row game published under Deep Silver as they purchased the IP in THQ's collapse.