Your argument is quite sensitive to the numbers, and your estimates of the numbers are questionable. Maybe someone from CMU CS is starting with $90k, but everyone I've talked to has offers significantly higher. Two of my closest friends have starting offers over $150k. Instead of spending their time sharpening how quickly they can map the shape of a button to the appropriate API call, they acquired deep knowledge of computing, and thus can do things in an hour most people couldn't in a month.