Vancouver firms can offer less pay because there aren't many alternatives when it comes to Canadian cities for a tech worker. Let's see...Toronto, Montreal, Waterloo and Calgary. And the winter weather east of the Rockies is horrible.
I agree, as the only Canadian city west of the Rockies Vancouver employers seem to think they don't need to compete with Toronto/Montreal/Calgary pay. And to a certain extent they're right. But with more and more US firms hiring Canadians on TN visas, the new competition is Seattle/SF.