I feel some of these results may be misleading. I watch YouTube mostly through Wifi, where the Wifi is the bottleneck and and not my ISP. The methodology page [1] doesn't seem to take that into account.
Well they are showing only ability to maintain a HD stream, not absolute speed. Any decent wifi network should be able to get at least 10mbit, so it won't impact HD streaming.
[1] http://www.google.com/get/videoqualityreport/#methodology