[freeasinfree]

They mention this in the fine print:

These ratings reflect the average performance of all Netflix streams on each ISPs network from Nov. 2012 through Jun. 2014 and average performance during prime time starting in Oct. 2013. The average is well below the peak performance due to many factors including the variety of encodes we use to deliver the TV shows and movies we carry as well as home Wi-Fi and the variety of devices our members use. Those factors cancel out when comparing across ISPs, so these relative rankings are a good indicator of the consistent performance typically experienced across all users on an ISP network.

If an ISP is averaging higher than 3 Mbps, then their users are either watching more Super HD streams than the rest, or are able to watch Super HD more often than the rest. Of course, they don't include that data.