> I don't see any reference here to IDFA being combined with browser cookies?

You should read again. Under "Determining Unique Users" you can see they link every "device id" to a unique user ID. A device id can be a browser cookie, an Apple IDFA or an Android AdID.

> Apple took this step without needing to be pressured by consumer rights groups.

Well, Apple is a smart company and better than most others with privacy. They may have concluded for themselves that they would probably get under pressure for this.