My reaction from reading both your original pitch and your revised pitch is that you were being quite vague. PG knows about the problems of collaboration, limitations of current tools, etc, you don't need to sell him on the existence of pain points. What you do have to sell him on is how your tool is uniquely suited for solving these pain points, which is what I missed entirely in your blog post. His interview style is to cut you off when you are telling him things that he already knows or when you are being to vague. He will force you to be specific and drill down on the points of your idea that are most critical.