The debate is silly since it is not really a debate about the same thing. It depends on where you draw the cost boundary. The OLPC project defines the boundary at the "retail" price of the computer itself. The critics are drawing a much larger boundary that includes maintainance, etc.
One side cannot change the conditions of the measurement and then claim that the other side is wrong.
How much does a car cost? Well the sticker says $10,000 but to drive it off the lot with delivery fees, dealer prep, sales tax, etc. it will take much more than that out of your pocket. And then it takes gas, oil, insurance, tires, etc. So how much does it cost? Depends on where you draw the boundary and what you care about.
The discussion is fine but argument about this is a waste.