I've been in the PM organizations at Google, Microsoft, among others. Now I'm a founder of my own startup.
At startups, we can see and effect the end-to-end of the business much more easily than in large organizations. The perspective, coupled with a business that is continually challenged to justify its existence, forces PMs to be great. Especially in these 4 areas: end-to-end business model innovation, networking, storytelling, and thinking big.