- Romney believes the right to abortion ought to be preserved in cases of rape or when there's a threat to the mother's life. - Obama hasn't endorsed raising the Social Security retirement age and campaigned against in 2008, but seemed willing to consider the idea as part of a compromise solvency package during the Bowles-Simpson negotiations. - Obama flat out supports lowering the corporate tax rate.
Also, when someone lands in the middle zone, it doesn't really make sense to say they should vote for a 3rd party as virtually all 3rd party candidates are either to the left of Obama or the right of Romney.
I went off what's on the website of both candidates - not various statements they may or not have made (which would be impossible to nail down, you say Nuance, I don't know if that's how I'd describe both parties pandering).
Romney on Abortion - "I am pro-life and believe that abortion should be limited to only instances of rape, incest, or to save the life of the mother. I support the reversal of Roe v. Wade, because it is bad law and bad medicine. "
Obama on Social Security - doesn't mention raising the age, Romney has it as part of his official platform
Obama on Corporate tax rate - again doesn't mention it was part of his plan, Romney has it as part of his official platform.
On the middle zone I agree which is why it's not presented seriously.