(To put it flippantly: I live in L.A. People who "do what they love" without being good at it are the ones who bring food to my table. I don't mean that in a derogatory way - I just wish they took their actual talents and ran with them.)
Again, there are other factors in play, but mastery is definitely important. I love running, I run everyday, but I'll never be a professional runner because I lack the skill and determination required to be a master runner. I don't even know if I'll ever be a master at anything, but I do know there are areas where I have a decent shot at it, so I know where to spend my precious time.
In the case of developers it may mean that you never become a master at programming, but what's more important: solving a problem or having elegant, well documented non-solutions?
Hackers make things work, and I think that's more important than being a "master" - I don't even like the word master, it almost feels egotistical.
A master of his art has the time to design not just his solution, but the task itself, and the experience to understand all the implications of a given solution.
And the issue is not finding people who don't enjoy what they're good at. I agreed that that might be quite rare. (Although there are definitely moments in every career where you hate what you do. It's inevitable)
It's that people abandon something they do enjoy, because it is not what they think they love. It's easy to love from afar, when you have only a passing knowledge. The hard work is keeping the love alive once you get intimate knowledge, in relationships as well as in jobs. So if you start with something you do well, you start with something you already know intimately. It's much easier to keep that working for you than building a new relationship, so to speak.
Some people will happily choose to wait tables in order to do what they love. Ain't freedom grand?
Fortunately it's a choice most of us get to make. If you're good at something, but hate doing it, you can still do it for the money. If you suck at something, and love doing it, you can do it anyway and suffer financially (and perhaps get better at it and then make money). It's a question of priorities.