It's likely the average of people in the US who have run the speed test.
Seriously. I wish I could get 10mbps internet at home...I haven't been able to do so in almost 10 years of living in a very big city and the suburbs of another very major city...
Same. What about all those people still on 1.5-6mbit DSL, or... shudder dialup?
I think most people have cable, which sometimes gives pretty good throughput.
I value customer service over raw speed, so I have Speakeasy DSL. It's not the fastest, but it is always up.