I think you're mostly right, and your example (sales work with big companies) is well aligned with your theory, but there are plenty of schlepps that are not conceivably anyone's passion because they don't require any differentiated work. My personal favorite example is a service that will perform DMV operations on your behalf (where the primary work involved is standing in line). Whenever I need that service, I am ecstatic to pay the $50 or so that they demand rather than lose rand()*4 hours of my day.
Similarly, while someone somewhere is probably excited to work on Stripe's fraud and security problems, I suspect there's a ton of paperwork that must be filed and waited-upon in order to operate such a service legally. I know plenty of lawyers and none of them consider that sort of thing fulfilling work.
I think there's a strong correlation between hard problems and intelligent people being passionate about them.
You probably won't find many intelligent people that are particularly interested in standing in queues, driving a cab or waiting tables. That's because these aren't hard things to do. On the other hand you'll find surprisingly many intelligent people that are passionate about how ants build nests, how quasars work and how to solve a rubiks cube because these are hard problems.
I've seen people post "Stand in line for me at the DMV" on TaskRabbit. I haven't tracked how many tasks, but it would be interesting to see growth over time. I wonder how that compares to the specialized services.
There are plenty of people who'd happily stand in line for $10. I'd do it; give me a usable queue computing device and I can do other stuff at the same time.
Similarly, while someone somewhere is probably excited to work on Stripe's fraud and security problems, I suspect there's a ton of paperwork that must be filed and waited-upon in order to operate such a service legally. I know plenty of lawyers and none of them consider that sort of thing fulfilling work.