OSX is not that much fun on a small screen, my macbook 13" requires me to have small dock icons and even then screen pace is still an issue, with Linux your can install a version of UNR and screen space is not an issue.
You do realise the link you posted (which I posted at the top of the article, btw) shows the two notebooks you quote as being the best, are not in fact fully compatible? Check the top of the chart: Dell Mini 9/Vostro A90, Eee 1000H, and HP Mini 1000 are all shown as working out of the box.
If he buys Mac OSX he should be able to run it. I know Apple doesn't allow it but unofficially at least he should be able to - if he wants. It's also not illegal in terms of criminal law - it's more of a breach of license. It's not a criminal offense.