While I'm not a fan of the cable companies, we do need to have some respect for the physics. As more and more customers are streaming movies with an "all you can eat" package, the ISP's facilities are being stressed. There is a big difference between delivering peaky traffic such as web pages, emails, social junk, and delivering steady HD video streams. There can be choke points between the NETFLIX server, major distribution nodes to the ISP, the ISP's facility, and the last mile to the customer.

A speed test result is a crude figure of merit for this sort of drama because the path for the speed test is likely different from the movie path.