They took free bsd made their own OS. Have they given back to BSD? Not in any major way. Sure they released Darwin but now they started keeping parts back to stop hackintoshes.  They took KHTML for webkit sure they release source as required but they don't contribute upstream.  So they embrace and extend but so far they have only taken from places that are so impoverished that their is no point to extinguish(desktop freebsd, KHTML user share?)