1. Being able (or expected) to enjoy your work is a relatively new thing in human society.
2. There's a set amount of people who will be passionate (or not) about their work no matter what, and for these people it's more about personalities or culture. I am thrilled to do software development, but I would also be thrilled to work in a coffee store. I'd also be thrilled to make pizzas all day, every day, or to push carts around a parking lot all day and help old people load their groceries. I've loved every job I've ever had, from landscaping to tutoring. How do the "Me's" factor in to this percent?
So I wonder two things:
How many people would say they are passionate about their work 100 years ago? 200? 300?
What are the bounds that it can reasonably be? In other words, whats the least and most it could reasonably be in a population? Even if everyone were farming serfs, whats the % going to look like? Will it be around 82%? More? Less?
I have a strong suspicion (cultural?) attitude and economic conditions (are you being taken care of? good food/healthcare/places to go?) has a lot more to do with it than anything else.