good graces

Today I was offered the chance to teach a six-week summer course; it's offered by my department every year and often serves as a chance for more advanced grad students to get additional content-based teaching experience (as opposed to teaching writing) before going on the job market. I very likely will graciously decline, and emphasize that I'd love to teach it next summer, for extra-academic reasons. (I'm more likely than not moving over the summer, and in general would prefer to have some time out of the classroom, especially because the first summer session begins quite soon after my responsibilities here (including singing) end for the semester.)

I've been thinking about the fact that I was offered the job in the first place, though, since there's at least one other person with more seniority in the department who'd be qualified to teach it. As best as I can figure, it would be a "reward" from the department chair for being responsible about things like paperwork and taking qualifying exams on time -- a biggie in my department, which (like every other dept.) is really feeling pressure from the dean's office to speed up time til graduation. No faculty member in my department has seen me teach, or, as far as I know, seen my mid-semester evaluations from this year, although I do know that my responsible behavior (again with that word) TA'ing last semester has reached administrative ears. I suppose I'm just wondering about cause and effect - should responsibility and punctuality imply that I should be offered a teaching job? If not, what should?