He stated "average bicycle pace", not average competition bicycle pace.
Going 20% faster on a bike relative to 12.5 mph requires more than 20% more effort, too.
8 is also 20% of 40, so 20% faster is like the difference between a ho-hum 48 minute time for a 10 km footrace, versus just cracking sub-forty. 20% faster can be a huge difference in fitness level.
And, anyway, Wikipedia helpfully explains (http://en.wikipedia.org/wiki/Bicycle_performance) that the average urban bicycling speed in at least one city is 9.8 mph. Not that that matters in any way.
Nevertheless, 20% is significant in bicycle speeds. It's not the 20% which is making this whole thing irrelevant. :)
If you've got that kind of a background 12.5mph doesn't feel right. So maybe not entirely pedantic.
... something like straight up into the stratosphere?