When you measure the people visiting say, Wikipedia, then you are only measuring the market share of the people visiting the wikipedia website.
Besides, this is about security. Ubuntu is known for its enterprise OS for a good reason whether you like it or not. It is very secure.
That's not to say that Linux Mint isn't secure either. But a lot of you are ignoring the massive manpower that Ubuntu has over Mint and they simply would not be able to release every new version that comes out without breaking something.
But then you guys miss a bigger point that someone just gave, "It's only as secure as it's operator." So shut your faces now, you trolls.