Because it's in natural language? WolframAlpha demonstrates (unsurprisingly) that it's still finicky. You still have to do just as much work to ensure connected services are working together properly.
Because--according to universal computation--it covers the entire computable world? So does any Turing-complete language.
I do see this as another cool thing along the lines of IPython Notebooks or JS Fiddle where you can quickly hook up to services and share the results. Uniquely, WolframAlpha's datasets and some of Mathematica's features. So it'd be nice for homework sets or Bret Victor-esque reactive documents (see http://worrydream.com/Tangle/).