All things being equal, there is a 2/3 chance that that next Google won't be happening in the US.
In this case, all things are not equal. Being located in the US and specifically in Silicon Valley makes a lot of venture-backed startup life easier, whether you need cofounders, investors, advisors, or employees. It's not a coincidence that Google, Apple, Facebook, LinkedIn, Twitter, Zynga, and Yahoo are all in the same area.