I don't agree with David. It's easy to say that the tablet was a low hanging fruit now, but before the iPad the very concept of tablet did not exist… Apple took a huge risk in launching a completely new product category, which became mainstream. We should also remember that people were laughing at the idea of Apple making a phone, as the market was already taken. What Steve's Apple did, at least three times (let's not forget the iPod), is to create new markets.
Apple might do the same with the next product. Maybe you'll wear it on your wrist, but I doubt it will be a watch.
It seems to me that with phones and tablets, Apple has already taken the low hanging fruit.