If I cleaned houses for 8 hours per day, 5 days a week, in the USA or Japan, I would make more money than I do now. Les Stansbery (a local friend of mine) used to do adjunct teaching at OSU branch campuses. He was a conscientious adjunct who made many corrections & suggestions on student papers, spent much time creating lesson plans, etc. By his calculation, his monthly paycheck, divided by the hours he spent on work, went below the minimum wage. Much of undergraduate teaching in American institutions of higher education is performed by "Teaching Assistants" (a misnomer because many TAs are entirely responsible for courses they teach) & other non-tenure-track instructors.
If money were the only or even main incentive, no one would study English, History, Philosophy, Sciences, etc., at least not _in Ph.D. programs_. Why not study Law, Medicine, Finance, Engineering, etc. instead?
According to Barbara E. Lovitts and Cary Nelson, "Although comprehensive national data do not exist on the consequences of graduate students' abandoning their degree programs, forty years of studies suggest the long-term attrition rate nationwide is about 50 percent. That rate may have increased somewhat in recent years, partly in response to the job market for new faculty; in any case, the news has certainly not improved. Moreover, the average national rate of attrition from Ph.D. programs disguises the reality in specific universities and departments" ("The Hidden Crisis in Graduate Education: Attrition From Ph.D Programs," _Academe_, at <http://www.aaup.org/ND00Lovi.htm>). The attrition rate has probably more to do with the poor chance of getting a tenure-track job than the average wages of tenured professors (which aren't shabby though they are by no means extravagant except for a few star professors), as well as the difficulty of combining teaching so-called "service courses" with research & writing while studying in a Ph.D. program that pays miserable "stipends."
I believe that the working conditions of tenured faculty cannot be maintained, much less improved, while an increasing portion of undergraduate instruction is being conducted by non-tenure-track teachers. Tenure has already been attacked by such means as enrollment quotas (at some community colleges, you need to make the quota or else your "tenure" gets taken away, e.g., Seminole Community College where Michael Hoover teaches), "post-tenure reviews," etc.
Yoshie