Helmets are definitely "the norm" here in Australia ... most people use them. It just looks normal to see cyclists with helmets. And both Rowan and I have numerous helmets to match our different bicycles or jackets.
We were in Canada for 3 weeks recently, and most of the cyclists I saw were wearing helmets, but not "most" like in Australia. "Most" in Australia = 90+% of what I've observed. "Most" in Canada = maybe 60% of what I've observed. Just my observations. BUT I had a bit of a chuckle at my reaction when I saw the first Canadian cyclist without a helmet ... my thought was, "What are you doing?? Do you really want to risk a ticket like that??" but then I remembered ... it's not illegal to ride without a helmet in Canada.
It's so easy to get into the habit of using a helmet, especially if everyone around you uses a helmet, it seems perfectly normal to wear one.