While I agree listen to lectures is often boring and I'll even admit I was one to frequently skip lectures from classes I didn't give two flips about (I'm thinking of you Philosophy!) - they can be really good for explaining things.
Some professors just have the gift of really good explanations. I'm sure you've had one of these. You know, the prof who just made things "click", had good lectures that made you go "ohhh like that? NOW i get it..".
At least I had a few of those. Lectures can be great - assuming it's from a good prof and it's on a topic you are actually interesting in
No, but they're the missing piece. People could already buy the books on their own if they wanted. Now the only thing people won't get for free is personal help.