Mitt Romney releases 2nd year of tax returns - how does he compare to current & previous Presidents?

Folks can defend him all they like, but it really does raise some eyebrows when you realize that:

• Mitt's own father, George Romney, released 12 years of tax returns
• George H. W. Bush released 19 years of tax returns
• Bill Clinton released 16 years of tax returns
• George W. Bush released 13 years of tax returns
• Barack Obama released 12 years of tax returns

But Mitt Romney only releases 2 full years of tax returns.

Don't you wonder why? Legal or not, what could he be hiding? And seriously, compared with all those other Presidents, doesn't it seem strange?