There is a crossover point. The issue is not mainstream would generate more. But to say enthutiast aint highly profitable is wrong. AMD would want to be there aswell, but they cant really.
A 8800GT is more like 150-180$ and the 9800GTX 290$.
Asume the production price is about equal. Maybe add 10$. Then it depends what nVidia earns on a 8800GT. If the GT gives 10$ profit and the GTX 120$ profit you would quickly need a alot higher revenue. For Intel the 1499$ chip cost the exact same to make as the 266$ chip. Enthutiast part of the game is basicly like milking a golden cow. Its free more or less with extremely high profit.
Oh, and the ATI part still doesnt make any profit.
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