There's a thing in the culture of road bikers about when you do and don't greet another cyclist on the road as you pass going opposite directions. Basically, if you're out on the open road where there aren't lots of riders, you wave or nod. If you pass close or are really out in the middle of nowhere, you yell hi. On city bikepaths, where you expect to be passing folks all the time, you never greet. When it's bitter cold, like -15º F, you might get a quick nod or an index finger lifted off the handlebar, kind of 'ah, another hardy soul'. So, the amount of acknowledgment of other riders is inversely proportional to the amount of bike traffic.
This morning, the streets were pretty empty of cars, with blinding snow and rapidly deteriorating conditions. Riding to and from hockey on city paths, several people said 'hi' and everybody was acknowledging each other with a nod or something. And there were still plenty of fresh bike tracks in the snow.