Let me put it another way. I can understand why a CEO might choose that, but as a user (especially as a user trying to find an answer, or a noob programmer trying to understand something better) all I would ever get was, "Hah! We've got answers .... and you've gotta pay."
My reaction was the same reaction we have when Google tries to foist G+ real-names on Youtube accounts, or when I see Quora's hidden results: "Oh, screw you!" It's not logical, but it's the feeling I (and I'm sure others) feel.
Quora is actually good, in that at least the first answer (usually very good) is usually visible, but as a user it's easy to see why I would want to use StackExchange rather than Experts' Exchange. I see all the answers, and am free to lurk. As a student, I would have been able to learn a lot about best-practices, or why X doesn't work with Y, where before I was stuck in ignorance due to not being able to justify the $ on a membership.
The main reason I turned to Wikipedia and Stack Overflow is not because they rank well on Google, but because they are free sources of information. Moreover, they don't constantly pester me to sign up, log in, or pay them anything. (I actually have an account at SO, but haven't posted anything: I don't feel like an expert on anything enough to write an answer that would actually earn points.)