While I was running this morning, the bicyclists wouldn't address the runners. I got passed once by a guy who had no light, said nothing, so I had no way of knowing he was there. At 6:20 am, in the dark, it is pretty surprising to be passed by something so quiet.
But when I would cross paths with a bike, I'd say "Morning." And they'd just silently go by.
The guy on the recumbent bike said, "Good Morning!" But he was a cheerful type and had a big, bushy white beard like Santa Claus.
The guy who was walking, but out of breath raised his hand in a gesture of a greeting.
The group of like a dozen (I couldn't tell because there were too many headlamps and runners with out headlamps) women running all said "Good Morning", too! :)
It was just the bicyclists. In the past, I've had some that greeted me. Heck, I've even got several friends who are bicyclists and they are quite friendly. Maybe these just aren't morning people and they are focused on their effort.
On a related note, since I've started working out regularly, I've noticed a marked improvement in my running. This morning was a great run.