While I don't want this to be about politics I do think a discussion of public policy might be due here. It isn't clear that Sarbanes-Oxley, high corporate taxes, a more and more unfriendly business environment is part of this.
If one looks at it more and more IPOs are going to places other then the US. While regulation has its place it is possible to "kill the goose that laid the golden egg" and I am not sure the US isn't there already.
Aon moving might be just another example of the US refusing to see we are making it hard for businesses to do business here.