I don't see why they should be bothered. If you look at the graph you posted, you can see that iOS is the second fastest growing product in tech history. Every year so far sales of the new iPhone have increased over the previous version. The same can't be said for high-end Android phones, for example the Galaxy S4 was a sales disappointment, causing Samsung to focus more on mid-range phones.
Android is only so prevelant because it is free, so manufacturers throw it on everything they have instead of having to make their own.As you can see from the profits of each company, most people want an Apple or Samsung phone, with the rest going for something cheap. Not many people go out looking for an "Android" or "iOS" phone. Most decide whether they want high-end or low-end based on their budget, and the majority of people going for high-end (which has far higher margins) end up with an iPhone.
Have a look at this: http://www.forbes.com/sites/tonybradley/2013/10/29/apple-can-ignore-android-market-share-stats-all-the-way-to-the-bank/
Android Market Share in 2007: 0%
Android market share right now: 81%
android marketshare in 3 years: above 90?
iPhone sales can increase all the way you want, if android keeps gathering marketshare, ios is going down eventually. The problem here is that you have a handfull of phones and 2 or 3 tablets on the iOS side, battling an OS fight against an horde of other devices. And if android is free, that's not a problem for google it seems. Thats also not a problem for angry birds :)
And I would like to see your source for the bolded. Because high-end phone on iOS means the latest from apple. 5C is mid range. High end on android means a plethora of devices.
So compare the sales from iphone 5S, with the sales of high-end android phones from: Xioami, Samsung, HTC, LG, Asus, Google, Sony, Motorola, ViVo, ZTE, Oppo, and that's enough to prove my point.
Do you think iPhone sells more than all of those combined ?
Nope, it doesn't. That's why android has been skyrocketing. It's not about a single overpriced device. It's about an OS that fits in every piece of hardware. Like windows many years ago.