Look at Apple. So many competitors have sprung up based on features that are missing in the existing products. Apple still win the consumers.

It's more than adding features to a product.

I suspect Facebook is easy to use because people can see the benefit in learning how to use it. They can see how tagging an image is a cool thing, so they'll make the effort. If they can't immediately see how upvoting a question is a cool thing, they won't bother to understand how to use it.