If you are comparing his effective tax rate as a percentage of his wage income then it is probably several thousand percent rather than 2%.
As for your assertion that his effective tax rate is only about 2%, based on your errant calculation of taking the difference between the FICA rates on wages and his estimated 15% effective tax rate, are you being deliberately misleading or just ignorantly misleading?
No, I'm not because Mitt Romney does not have a "wage" income. Probably never did. I'm comparing the income from all sources from Romney and the income from all sources for Joe Six Pack.
Joe Six pack making $20 an hour has a minimum effective income tax of 15% just by his FICA contributions and probably another 15% tax on his earned income making his overall effective income tax rate somewhere in the neighborhood of 30%. So the headline is clearly misleading.