Why? Because without this blanket waiver it opens them up to all kinds of legal issues since a core mechanic of their site is re-pinning.
If you upload a photo to their site and someone else re-pins it, did that person just violate your copyright?
If Pinterest implements a "most popular pins" page and features one of your photos on that page, did they just violate your copyright?
Yes, you can come up with legalese for each potential scenario, but it really does complicate things. It's easier for them to just have a blanket clause and act in good faith, than open themselves up to the possibility of accidentally using someone's work in a way their ToS didn't whitelist.
Be explicit about what forms of (re)distribution are allowed instead of going for a blanket license. Where appropriate, also be explicit about what is not allowed.
It shouldn't say much more than "you give us the right to use your content to fulfill the services you ask us to provide, and you have the right to remove your content at any time."
I guarantee that every site you use which involves UGC has a similar clause in their Terms of Service. You're living in la-la land if you think that's going to change, honestly.
More important than the terms is the character of the founders and the company. Do you trust Pinterest to do right by you? Flickr has a similar clause, for example, but photographers still trust them.
If you don't trust Pinterest, that's fine. But in that case, do you really think changing some words on one of their pages is going to make a difference in their overall behavior?
Yes, I see you are right. I guess it seems like I'm more likely to run afoul of the clause with Pinterest. Youtube is like "Funniest Home Videos," Pinterest has gallery like qualities.
Your examples after the link don't seem to have much to do with selling the works though. In Youtube's case, it's to allow them to advertise with overlays. Maybe that is where Pinterest is going as well.
See for example section 6.C in YouTube's ToS. http://www.youtube.com/static?gl=US&template=terms
Why? Because without this blanket waiver it opens them up to all kinds of legal issues since a core mechanic of their site is re-pinning.
If you upload a photo to their site and someone else re-pins it, did that person just violate your copyright?
If Pinterest implements a "most popular pins" page and features one of your photos on that page, did they just violate your copyright?
Yes, you can come up with legalese for each potential scenario, but it really does complicate things. It's easier for them to just have a blanket clause and act in good faith, than open themselves up to the possibility of accidentally using someone's work in a way their ToS didn't whitelist.