That's the first time I've heard that one. Most believe it's any or all of these reasons
No doubt the notebook processors were a big reason why, but free Linux is eating *nix's lunch in many cases, and that includes OSX. Solaris can now go toe to toe on Intel, and so will OSX. Not sure how you never understood what was going on, when two of the most well known journalists covering Linux and Apple were all over it.
http://www.eweek.com/article2/0,1895,1824810,00.asp
http://www.marketwatch.com/News/Story/Story.aspx?guid=%7BD0E8469A%2D28FC%2D415D%2D9281%2DC97B5FA2CA3D%7D&siteid=mktw&dist=nbs