Some more numbers to look at

http://dougsarchaeology.wordpress.com/2012/02/21/how-much-full-archaeology-professors-make-breakdown-of-numbers/

Doug -

  One thing that seems to be missing from your numbers - part time adjuncts (because the school won't hire anyone full time). 
I have worked at three different locations as an adjunct - and have been asked back at other times to each of them.  In addition to myself, at least two of the schools also hire other adjuncts - to teach classes that I could easily have done (and in fact had done in other years).  While hiring a single person full time would seem to be productive in a lot of ways, it woud also mean the need to pay benefits, vacation time etc.  all of which costs the school more.  So instead of hiring a single full time adjunct - who could teach 6 classes/year and cost them $43,000 (from your survey) plus benefits, etc.  they hire three adjuncts for one class each per semester, and pay a total of $12-18,000 for the class coverage.  To add insult to the injury - the adjuncts all have to share offices (at one school I shared it with 22 others!). 

I always understood this and kept going back, despite realizing what poor treatment this was, simply because I loved to teach. 

The numbers are for full time but in most cases, as you mention, they are all temp. Some of the prof, asst., , and associate are also part time. The numbers just need to be adjusted for actual work.

These numbers are just suppose to maximum earn, actual is a whole other story.

In my research I came across some numbers on benefits. I will look it up and put something together on it as I remember benefits could add $10,000s to a persons' "cost" to the university.  There is a definite reason they don't make someone full time.

More information, this time for associate professors here

And some information on assistant professors.