[msnimje]

How is calling her his grandmother inaccurate? ....Is a step father not a real father?

Most people understand the use of the word "real" to mean "actual" or "factual" when used in this manner.

Semantics will not change the fact that this woman was a wife of his grandfather rather than his grandmother.

[Sols]

This is silly. A grandmother is a grandmother, they don't have to be your biological grandmother. They could be married to your grandfather or they could be the mother of your stepfather or they could have adopted your father but the maternal figure of one of your parents is your grandmother.

I'd hate to think what title we'd be trying to insist she be called by if she had adopted his father. "The adoptive mother of Sen. Obama's biological father.." is quite a mouthful.