It's even more impressive considering how hard it is to beat
all the other Android phones with similar specs in the market, too. The switch from one specific Android phone to another is so much easier than from an iPhone to an Android phone. In this regard Apple has much less direct competition.
So when one phone reaches iPhone-level numbers, despite the fact that you could easily replace it with another similar specced Android phone, it makes it all the more impressive.
That being said, as an Android user, I don't really like this outcome. The fact that one Android manufacturer is getting close to Apple's sales numbers is pretty meaningless to me, and the fact that one Android manufacturer can sell 50% of Android phones is actually pretty worrisome. I'd rather have 5 top manufacturers with 15% or so market share each. Apple users may be fine with an "Apple monopoly" in the iOS market, but I'm not fine with a Samsung monopoly in the Android market.
But I guess it's all about the Pareto principle and other power laws like that, so it may be just a fact of life. At least it might be a lot easier to change who is the biggest Android company a few years down the road, if Samsung slips.