Hi Michael,
As I read your response, you almost exactly described a situation I found myself in during my college days.
When I was in high school, playing the piano was my main hobby. I was also in a garage band, and in the school jazz band. All of my teachers, guidance counselors and my family were pushing me towards pursuing a career in music, because it was and is something that I love doing. So I went through all of the auditions for the various music schools and I wound up being accepted and going to a music conservatory as a college freshman. Music became my job at college. It required me to practice 8-10 hours per day just to keep up with my peers. To make a long story short, I was back home by the 2nd semester of my freshman year, attending a college near my home. I couldn't turn my love of music into an 8 hour, forced regimen. So, in that sense I agree with you, HOWEVER...
I have found through the past several years, that there are several things I enjoy doing to varying degrees and in varying ways. I've managed to find a career for myself, where I'm doing something that I enjoy in a way that I can do it AS A JOB. I was unable to do music as a job, because of my nature. Possibly, I enjoy music too much to do it as a job. What I think the key to happiness in one's working life is finding something that brings them satisfaction in a career context, not in a hobby context, if that makes any sense.
For example with me, I'm inclined towards using my creativity and the arts. And while I couldn't turn my love of music into a job, I found a career designing stained glass lamps, windows, entrances, etc. into a career that I'm highly satisfied with. It never gets boring for me and it never feels like a job.
I should have been more specific in my first post and said that I think the key is it to find something that you can be passionate about in a job context. I agree with you in that one won't get very far if they try to make a job out of something that they have a passion for in an enjoyment or hobby context - at least this has been my personal experience.

Joe Cooper