It looks good, and it is, but I think its becasuse there are still relativly few Apple models to choose from, compared to the dozens and dozens of PC models from many manufactureres. Apple has always had a good marketshare compared to any other individual manufacturer, but it looks bad when all the other manufacturers are grouped togerther under the windows umbrella.
If Amazon compared sales of computers with Mac OS vs all computers with Windows it would be a different story.
Still, it must give a good impression of Apple to people who don't know much about computers who see the list.