Verizon and Comcast have been sinking in Netflix's rankings for months. In October of 2013, Verizon FiOS was at 2.22Mbps. In January, when it dropped from sixth place to seventh place among the broadband providers listed, it was at 1.82Mbps. The largest single-month drop occurred between December and January (2.11Mbps to 1.82Mbps).
Verizon DSL users also saw four straight months of dropping stats, starting at 1.42Mbps in October and dropping to 0.97Mbps in January. The largest single-month drop again occurred between December and January.
Meanwhile, Comcast users didn't see a drop in overall rank -- it remained at no. 14. However, the ISP started at 2.07Mbps in October and dropped to 1.51Mbps in January. In Comcast's case, the performance drop seemed equally distributed between the months.
While there is still insufficient evidence to use throttling as a possible reason for the drops, the net neutrality issue still looms large. The January court decision means that if they so desired, ISPs could begin charging more for certain types of traffic, and slow those who don't ante up.
More likely, though, it's simply a reflection of increased Netflix traffic. In addotion, the declines in performance seem to have come after Netflix expanded its "Super HD" and 3D video to all customers, including those whose ISPs are not members of Open Connect, Netflix's content delivery network.
Verizon and Comcast, notably, have not joined Open Connect, which can improve Netflix performance by placing video caches closer to customers.
The graph above can be seen here, but you have to tweak the tool to see the exact dates and restrict it to only Verizon and Comcast.