Yes: it's harder than people think to divine what people will pay for and what they won't.
As a consumer, I pay for plenty of things I wouldn't necessarily have predicted I would; conversely, I use some "successful" services that I'll never pay a dime for.
Yeah it is hard for the founders to know what people will pay for ahead of time. In a few cases there they had free competition, although that may have sprung up after they started. If you have free competition and are looking for direct payments from users as a model you have to think you can build a much better product than the free alternative.
Something like Twitter I think is a great example of people probably not knowing they wanted it until they used it and it built up a bit. Sure they are ad supported, but Twitter could have very easily fit into the type of stories in this post had things went a little differently.
As a consumer, I pay for plenty of things I wouldn't necessarily have predicted I would; conversely, I use some "successful" services that I'll never pay a dime for.