The problem is your numbers are terribly wrong in multiple ways. I don't think people have mentioned that not every subscriber is online simultaneously or that most are still watching 1080p.
Your argument is at least as wrong as mine, though, while you seek to reduce the numbers, you are not also seeking to increase the scope of the cost from JUST the hardware depreciation and monthly fiber cost of the interconnect to the actual cost of the interconnect. The point is, it's not even close to "negligible"