An excerpt from President Obama's Proclamation on Mother's Day signed earlier this week:

NOW, THEREFORE, I, BARACK OBAMA, President of the United States of America, do hereby proclaim May 8, 2011, as Mother's Day. I urge all Americans to express their love, respect, and gratitude to mothers everywhere, and I call upon all citizens to observe this day with appropriate programs, ceremonies, and activities.

It's a beautifully written proclamation but he stuck to the idea that mothers are only female mothers and grandmothers... but we all know mothers come in many different forms.