It's one of those things that I think companies know about and do but doesn't want to talk about it. Keep tabs on their users is a gold mine for companies. Companies like Google and Facebook want to be able to know what we're up to and how to best monetize that information. Others like carriers might want to know how to best optimize their networks.
So why does Apple want that information?
It's too soon to tell. Supposedly, this information isn't something new and have been covered in the past without fanfare until a couple of security "experts" decided to bring it to our attention.
Personally, I'm not worried - not yet. And it's not like this information is something that Facebook, which is a lot more dangerous to privacy, will ever get it.
Still, I want to know why Apple is gather this information. Supposedly, it could be a bug where information were not purged as it was supposed to. And yes, Apple can ("is" to some) be evil so we'll need to watch this closely. At least we know that they're not selling out info to the highest bidder like others who make their living off selling advertisements.
According to WSJ, Google is doing it as well. So it doesn't make any better.