For whatever reason, the culture in Silicon Valley has evolved to be relatively open about ideas and business plans. As you've discovered, this is a stark contrast with the norms in lots of other industries/parts of the world.
This culture of course has a powerful pro-economic side effect -- ideas that are shared have a chance to grow, evolve, be challenged and fork, ultimately coming out stronger and better-developed.
To answer your concrete question on how to persuade someone with a different background to open up about their ideas -- maybe share this blog post with them? A little bit of social validation that other successful people are willing to share their ideas can't hurt. :)
This culture of course has a powerful pro-economic side effect -- ideas that are shared have a chance to grow, evolve, be challenged and fork, ultimately coming out stronger and better-developed.
To answer your concrete question on how to persuade someone with a different background to open up about their ideas -- maybe share this blog post with them? A little bit of social validation that other successful people are willing to share their ideas can't hurt. :)