Instead of paying somebody once to do this stuff with skrollr, you instead rent your own website from this company for the rest of your life? Good business plan for the rentier.
As someone who has many years of experience coding animations by hand in css and a little js, sometimes a tool would be more useful. Its too easy to get lost in the minutiae of the code and lose sight of the visual impact you're going for.
For some people, a tool like this is entirely worth the cost.