year-round is not the same as all-weather
There is a difference between year-round and all-weather.
Here the weather is intermittently nice enough all year that plenty of people ride year round (both commuters and recreational riders)*. On the other hand we do get spells of sub-zero weather and snow. The number of riders certainly is less, but I do see tracks and other riders in even the worse conditions. This is particularly true in Boulder where the bike paths are often cleared before the roads.
Paul
Just last week it was a high of over 60F and a low of -15F within a few days.