The main point might be that your parents aren't technical people (whatever that means), and the laptop was set from the start (they never had to care about hardware compatibilities).
We did a similar thing with my inlaws, leaving an ipad behind to facetime with their grandson, and recently they called because they couldn't see their new mails anymore (their provider changed the imap servers), they also happened to mainly browse sites on the ipad now, installed a few other apps for learning english and we don't hear about windows problems as much as before (they still need the laptop for standard Word/Excel/Powerpoint work and to print since they don't own a blessed HP model)
As you did we give them an opportunity to switch to linux, but they would need a well supported and preinstalled machine somehow, and that's not trivial to find. DELL seems to have some available on their net store, but it's a hard pill to swallow for people used to buy VAIO laptops in person and in store (not that they cared about the brand, but they look very nice and the sales person is reassuring).
Going the Apple route would bring more or less the same upsides as ubuntu, while skipping all the hardware support parts, giving real exclusive advantages (battery life etc), the bonus being they'd see anouncement in the press they'd understand what the fuss it is about. Linux could be viable, but it seems too late now that the Apple lineup is leaps and bound ahead of everyone else.