They do not[1] treat all their vendors the same way. It has been documented that Google provides early access to particular vendors, in order to suit their own desires for the launch of each version of Android. It has been going on at least since the original Droid launch on Verizon.
I guess it depends on what you mean by 'launch'. There was an ICS image released like a month ago, and a friend was running a CyanogenMod 9 alpha build shortly after.
