Re: What's the incentive for vendors to use this?
>If Google tries to lock things down too much, OEMs might not choose to follow.
So what? If an HTC get too big for their boots, there will be a Huawei or OnePlus (or a Bloggs MK1 with Qualcomm SoC, Sony camera and LG display... same difference) to fill their place. [please update my references according to how far through 2016/17 we are].
Speaking as a fan of the Sony Xperia Z (Compact) range, there is little that Android OEMs can do to differentiate themselves.
My friend is still using his iPhone 4S - and beyond replacing its battery himself, has cheerfully taken no interest in mobile phones since he bought it. He's vaguely 'normal'. I'm not, so I'll use my cheap (and seemingly indestructibly plastic) Huawei until I get a Project Mango Lenovo (Y'know, the one with the 3D depth mapping )