The internet is superior to a book in that the information is interconnected and browsable in any direction, much more easily than in books. And there's a lot of good reference material out there on the web-- Wikipedia alone is worth the cost of entry IMHO.
Then you have online learning sites, some of which have active as well as static content. That's something you just can't get from books.
I don't think the notion that learning can and should involve more than engaging in memorization of facts (which is also "real learning" of a kind, as intelligence depends in part on knowledge) means that reading and/or interacting with non-static content on the web or elsewhere isn't a learning activity. Austin's link is a good one.
The main drawback to the internet is, of course, danger, e.g. from inappropriate material and predators. But as long as use of the internet is made safe, I don't see much to argue about: in addition to everything else that a child can be exposed to for learning, the internet can be quite a useful resource.
