The first time I received Icebreaker, it was from a legendary engram. I bought a second IB this morning. I may buy a third before the weekend is done just so I can keep one assigned to each of my characters. Seeing as I had over 100 strange coins when I bought the second one this morning, I would say it was "earned" quite a bit more than my first one... And if I buy the third one, it too will be "earned." And I will still have 100 coins. I personally prefer getting them conveniently this way than waiting for another random drop. It's really, really hard to claim anything outside the unique RAID weapon/gear drops or Iron Banner (which I don't participate in) is "earned" in some way different than other equipment or weapons. There are so many different ways to obtain Icebreaker, what does it really matter if Xur's selling it is one of them?