If you've chosen to buy something from Apple, it's hard for Apple not to know that you've bought it.

I don't think that's an issue.

What is an issue is the cross-correlation of any given company's data on you with lots of other "big data" companies, building a profile, not just of what you've bought from X, but from Y, Z, hell throw in the whole alphabet, why not ?

Then there's the machine learning that says when X,Y,Z are all bought within a small time window, that means alpha is likely, and decisions can be made on that basis.

It's the spread of the network that is the problem, IMHO, not the knowledge per se. My butcher knows what cuts of meat I like, there's no need for my cobbler to be aware...