History of Software Patches?

NinaBeth asks: "I'm interested in the history behind software patches for an academic paper I'm writing. In particularly, I'm wondering what motivates shrink-wrap software companies to release patches? Why send out 'broken software'? Is it purely financial? Has anyone done a cost-savings analysis of QC prior to release versus user-reported problems? Any stats on the average number of patches an application will require? Is any one particular company more patch-happy than others? I don't need much, just a reference or two would be helpful. Thanks for any suggestions!"