As noted on Cnet's Buzz Out Loud , all for tax reasons - ah yes...
Not for partnering with other companies such as Google? Of course not.
Let's see...Mozilla provides a full cross-platform development environment with Xul and then Google provides the home page...who needs a GoogleOS? Would this be called Mozoogle or simply Goozilla?
Mozilla Foundation Announces Creation of Mozilla Corporation - MozillaZine Talkback