I've tested this on different sound (vibrate/silent/normal) settings and no matter what my phone does not vibrate when it powers off.
I'm not sure when this started, i.e. if you're going to ask me whether this stared after an OTA or something
I remember some time in the distinct past it used to vibrate, and the nexus 4 and galaxy nexus I had before most certainly did that as well.
My phone still vibrates on all other occasions.
I am fully stock (4.4.3 KTU84M), rooted