For me, what was clear is that they listened to feedback and took action relatively quickly. I remember when they first launched the Blackberry version and emailing the team about bugs - I think I got a response the following day and they clearly implemented something by the following release.
It wasn't about being devoted to a vision of a particular product they were passionate about. They saw a market/ problem and solved it using their technical ability.
Yes, they had a lot of luck on their side - being in the market early enough to gain the visibility. Also, people naturally promoted the app so they didn't need to spend much on marketing. Other apps that came after it, weren't so lucky. Being well connected and having cash to provide initial runway probably made this easier for him than it would be for most but I think it's fair to say he built up his rep at Yahoo - which probably helped when he needed to raise cash.