For now, HAT is just taking copies of what is on Facebook. However, if you start using notables, and share only for 1/7/14/30 days, you will eventually come to a situation where you have all the words, but because it was deleted on Facebook, you might not have much on FB any more. That said, it does depend on FB policy. Do they really delete it? We can't control any of that.
To be honest, if you value the socialising and news feed on FB, then they are giving you a service so you would be 'paying' for it with your data. Of course, it may still annoy you since you don't have a choice.
At some point in time when all the data that sits in your HAT becomes more and more, you (us, collectively) would probably be in a better bargaining position on what they can do with it, but we need to get to that position first!
As to the app question, I will get back to you once I get an answer from our iOS team.