I wonder how much this reflects a split in the market between people who treat their smartphone like a computer vs those who treat it like an appliance. When I buy a microwave, a TV, a stereo, a car, or pretty much any other consumer product, I have no expectation that the UI will ever change. I won't have people moving the knobs on my cars dashboard, or "flattening" the UI on my microwave. Android is on OS used primarily by phone manufacturers who still want to control the user experience (e.g. TouchWiz), and who are selling that phone as an appliance.

Complaining that one can't put Kit Kat on a Nexus S seems a bit like complaining that you can't add HDMI input on your old Sony Trinitron or put ABS on my 1990 Miata.