> Built in obsolescence?
Compared to its competitors, decidedly no. The state of affairs on Android is even worse.
Samsung Galaxy S2 release: May 2, 2011
Apple iPhone 4S release: October 14, 2011
Google Galaxy Nexus: November 17, 2011
Galaxy S2 last OS release: October 9, 2012
4S's latest OS release: October 21, *2015*
Galaxy Nexus' last OS release: October 3, 2013
Compared to other industries, like computers or cars, sure. Maybe it's planned obsolescence.
Or maybe it's just that it's such a new product that innovations and consumer desire are faster than usual (or, likely, sustainable).
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https://en.wikipedia.org/wiki/IPhone_4S
https://en.wikipedia.org/wiki/Samsung_Galaxy_S_II