I agree. For consumer startups, it's not that important to solve a problem. As you mentioned, Angry Birds and Pinterest do not solve problems - they give us dopamine and entertainment instead. Consumer products need to be like crack, and you also need to be a well-networked crack dealer (marketing).
Entreprise startups do need to solve problems though, or at least help you make more money.
But nor do people pay for a lot of the fashionable consumer products such as Pinterest.
If people aren't prepared to pay then they do not have a viable sustainable business. They can keep taking VC investment and hope to sell to Google or whatever but thats a different thing.
I believe that if you solve a real problem that people are having, consumers will be more likely to open their wallets for it.
[Angry Birds is an interesting one. It's obviously a profitable franchise but the pricing model of mobile apps makes is such that they can be sold as a very cheap impulse buy. Micro payments perhaps make the model of building for desire rather than problem solving more viable.
Entreprise startups do need to solve problems though, or at least help you make more money.