You're right, there's no real association of that copy to your machine or anything like that, and no requirement to do so.
Probably helps with Apple's demographics tracking, etc. Also, they can target various marketing emails & such. It's also probably easier to include all their software in the process than those that may be serialized (if there's any left). I don't know if FCP, Aperture, or any of the other "Pro" apps still have it.