To be fair, Quora has made very little effort to compete in SO's area. In a sense, both sites were created to solve entirely different problems, albeit problems that traditionally occur in the same space...
- SO is the answer to the question, "How can we keep useful technical information from being scattered among forum chatter?"
- Quora is the answer to the question, "How can we keep interesting forum chatter from being scattered among... less interesting forum chatter?"
There are countless other takes on both of these ideas, of course. Sites like E2 and K5 could be considered spiritual ancestors, while ExpertsExchange clearly had a much more direct influence on the designs of both SO and Quora. It'll be interesting to see which one folks still remember in 10 years... And what then-current systems have learned from them.
Quora could have been so much more than it is, it doesnt look very successfull to me,because of stupid choices.