Ideas are worthless. It's execution that counts. Examples of "ideas" that were won by the best execution include:

Google (search)

Facebook (social network)

Microsoft Word (word processing)

Photoshop (image manipulation)

iPod (mp3 players)

iPhone (smartphones)

Each of these "ideas" had competitors in the market before them, and each managed to blow the competition away by better execution. This is the reasoning behind VCs not signing NDAs, and entrepreneurs accepting this.