> It smells like data mining to me; instead of building their own safe browsing service, why not just defer to Google's services?

I'm sure Apple doesn't need to build APIs to do data mining on their own users. It would be very un-apple to create an API like this and allow non-apple devices to use it. So where is the benefit on data mining?

Privacy (in a consumer and marketing sense) is a major market advantage. I think that Apple has determined that keeping data away from 3rd parties is a good way to capitalize on that market edge vs. giving up the edge and engaging in the same consumer exploitation as their competitors.