That's like saying it's unsustainable to continue to sell 1 gigabit internet for $70 a month...... Oh wait, Google fiber is launching in Austin in a few months..... or the $399 Nexus Q that the $35 chromecast does?
Google just reported $16.7 billion in revenue and $3.7 billion in profit in the third quarter of 2014! They benefit from ad revenue as their main source of income. They can sustain a little longer than one plus can.....