They're not complex in the Big O sense, they are complex systems in the sense that they have to incorporate and reconcile organizational knowledge from very dif

They're not complex in the Big O sense, they are complex systems in the sense that they have to incorporate and reconcile organizational knowledge from very different domains - e.g. Ron Jeffries' "Why Is Payroll Hard" http://wiki.c2.com/?WhyIsPayrollHard http://wiki.c2.com/?WhyIsPayrollHard - while working in a predictable fashion with implicit requirements on availability and consistency, which the average web app stack more often than not leaves as "someone else's problem"