The vast majority of people that live here do so because of the amazing array of wilderness outdoor activities on offer mere minutes from town. I've lived in a lot of places in Western Canada, and none of them hold a candle to Whitehorse in this regard.
I don't know for sure, but my guess on a bike riding stat is that there are a lot of people living here that are outdoor/fitness freaks. Most of them are super freaks.
Also, anyone that doesn't like the winter leaves. So those of us that stay love it, and we don't care if it's +30C or -30C when it comes to doing awesome outdoor activities :)