This must be based on the number of cyclists on the road, rather than a measure of the quality of cycling or cycling infrastructure. Groningen, Netherlands, or perhaps even Rotterdam - for example - appears to have a better / more modern (?) cycling infrastructure than Amsterdam, in my experience (granted I have not been through all of Amsterdam).
And while Amsterdam may have the most cycles, Copenhagen has been reported to have the most cycles *
in use on a daily basis* - atleast 400,000 cyclists going into and out of the city daily.
Sounds more like this info was based on articles like
http://uk.askmen.com/top_10/travel/top-10-bicycle-friendly-cities_10.html. And that appears to be based on a 2 year old article.
Other searches on the net list Dublin to be in the top ten as of September 2011, and Minneapolis, Minnesota as the best in the U.S. Several people who live in Curitiba, Brazil have balked at it being listed at all!
As with all 'surveys' that get copied and pasted from the net, you should take the results with a grain of salt. I suspect there are personal bests and worsts around the globe, and a city that is good for upright bikes may not be practical for velomobiles, or cargo-bikes - and vice-versa.
"Your mileage may vary" is worth keeping in mind.
