From a long essay about Google and Amazon by a guy who's worked for both:
Though the article's more about why Google's APIs are mostly crap. Now I know!
But I'll argue that Accessibility is actually more important than Security because dialing Accessibility to zero means you have no product at all, whereas dialing Security to zero can still get you a reasonably successful product such as the Playstation Network.
Though the article's more about why Google's APIs are mostly crap. Now I know!