I don't personally recall the four-AA revision. Wikipedia links to Apple's press release http://www.apple.com/pr/library/2003/09/16Apple-Introduces-W... which confirms four AAs.

My keyboard, bought in November 2008, part number MB167LL/A, definitely takes three.

Current revision available on Apple's website is MC184LL/B and that one is well known to only require two.