That's probably becuase the outer vents are seperate pieces and can be replaced by the chrome pieces you saw. The middle vents are part of the whole center console and until someone makes an overlay for the center vents your stuck with only the two outer ones. You can buy a whole center console in chrome so it will match the outside vents.
Go here:
http://www.autotrucktoys.com/ptcruis...P4226C619.aspx