Two Types of "A" Players

Why is it that there seems to be the assumption that all "A" players are those who live to work, work 60+ hour weeks, and generally immerse themselves with their work?

I employ "A" players who want to work 40 hours a week and spend the rest of the time with their families. They are excellent at what they do; they just want to do it as a job, not as a lifestyle, and they want to compartmentalize it into 9-5, M-F.

Why is that so hard to believe?