That's one step beyond believing an "independent, third-party" report commissioned by McDonalds to show that their burgers make you healthy or cure cancer or whatever. Basecamp is not even pretending to be neutral.
If you assume a company's lying, there's probably very little that they can say to get you on board.
But there are ways to present information that don't seem stupid. In particular, Basecamp is doing two things here that are misleading. First, they're not actually presenting data, they're presenting anecdote(s). Second, they're presenting them in a medium which should be viewed with extra skepticism.
I don't want to know what percentage of your paying customers like you (seriously? 3% of your customers use you but dislike your product?). What I want to know is what specifically you do and how you do it. Everything else is noise - and so the entire page is noise.
Still, I can understand why you'd feel that way, and I don't really disagree with you that that's more what I'd find interesting. But as to whether that's what most people would be interested in, and whether that's what would sell.... -shrug- I'm not sure that all attempts at sales makes you a con man. Trying to demonstrate to people who may not understand how a certain thing would advantage them that it would, or that people who are like them think it would, doesn't necessarily amount to a stitch up job. I can understand that you'd view it as noise, but it seems to me at the moment to perhaps be a little harsh to call someone who may just be trying to put the best foot forwards a con man when they may be operating in good faith.