Earlier quoted context omitted.
Absolutely, you need both. I'm not sure how to quantify which one is more powerful or important, especially since "idea" can mean many things, from a very vague concept to a fully fleshed out and vetted business plan. I was just taking issue with the "ideas are worth nothing, execution is everything" mantra.
Let me quote Derek Sivers: "To me, ideas are worth nothing unless executed. They are just a multiplier. Execution is worth millions." http://sivers.org/multiply
That to me is a more interesting and logical question.