Biography vs Autobiography

While I was reading Alan Alda's Never Have Your Dog Stuffed (review here), my wife and I started discussing how the book was labeled. It was called a Biography, both on the shelf and inside the the book. But we both agreed with what we learned in school. A biographical book written by the person covered was called an Autobiography.

So I now ask you, is the Autobiography from twenty years ago now considered a Biography? Is it like the transformation of "actor and actress" becoming "actor?" Was there some great legislation among the librarians that decided this?

I have never been a huge fan of non-fiction in general or even biographic books. But I happened to pick up and read two more that could have fallen into the Biography vs. Autobiography debate. First was Ghosts of War by Ryan Smithson (review here) and the second was The Hornet's Sting by Mark Ryan (review here). Both appeared to be marked correctly (Smithson's was marked as an Autobiography as he wrote it and Ryan's book was marked as Biography as it was about another person).

So was Alda's book just marked wrong? Did Alda have someone else write the book? Or are Autobiography and Biography interchangeable? I'm really hoping it's the latter.