most of the time, I would say yes. Being able to cast your abilities more often is crucial to gods whose chief source of dealing damage comes from their abilities. However, building 40% CDR is much less essential for gods whose primary source of dealing damage comes from auto-attacks (this goes for both AD and AP gods). That doesn't mean you shouldn't build 40%, but rather, if you want to get an item that provides you with more raw damage instead of CDR, it's not the end of the world since most of your damage comes from auto-attacks, not abilities.