Apple's business is not one that has to own a market to make gobsmacking amounts of money. As such I doubt they see being outsold by Chromebooks as being a serious problem; they've been being outsold in the laptop market forever and are still making yachtloads of cash.
And as to sustainable business models - the iTunes Ecosystem alone is a large as half of Google's entire business and is growing faster.
Most Chromebooks are glorified phone hardware. Even the one with the whizzbang screen has lousy soldered-on local storage, so it fails as a microcomputer. It essentially is a terminal with a fantastic screen. I certainly wouldn't attempt to use one to develop on (and I mean develop on, not RDP/VNC/SSH to a box elsewhere). Could I write C++ on it for multiple OSes thanks to virtualization on a Chromebook? I know my needs are niche but I don't think Chromebooks compete with MacBooks, even if they look similar-ish and one has outsold the other. Out of interest, have Kindles outsold MacBooks? Would that be the death-knell for MacBooks? Really is comparing Apples and Oranges I think.
Do you supplement the internal storage with external? Is it a hassle? My Windows VMs are all 50GB+ so having tiny internal SSD storage is crippling.
[1] http://www.ibtimes.com/googles-chromebook-outsells-apples-ma...