Immaterial would be a wrong word. Negligible might be better. Negligible right now would be perfect. Let's not be naive, they have a full advertisement department trying to monetize their platform and increase the revenue. They also tried to compete with Google for six years for the same, but failed in the in-app advertising. They are still trying to expand their advertising in other areas though:

http://searchengineland.com/apple-expanding-successful-searc...