As I understand it Chrome is not open source and that is why it is not in the Software Centre. Chrome will never be the default browser in Ubuntu because it is not open source. One day Chromium may be the default browser. It is a subject for debate but why create arguments. What I find tiresome is the repeated demands for personal preferences to be made the default.
I will vote against Chrome being made the default simply because I like to say no to people who demand that I accept their personal preferences.