Quite intriguing! I have no experience pitching to investors or advertisers, (but i do have web analytics exp.) and never would have thought that this would even be a question! Curious, is this something that you encountered, or is this hypothetical?
I had heard in the past that if your numbers were not GA, then they did not put much weight into them. Since you can grant access to other people directly into GA, they can validate the data. Using awstats or other metrics were deemed less trustworthy since they required someone gathering the data (which allows for potential manipulation). Before the days of 3rd party advertising, people tried to sell local ads just like a news paper. The website with more visitors could charge more for the ad banner space. Some "little" blog would have to prove they received the amount of traffic.
