Difference in turn in:

I just saw this. That just shows Hamilton turning into Rosberg though, and Rosberg not yet willing to give him more room that is required. Again, he's not required to put on the lock Lewis had, he only required to leave him a car's width, nothing more.
After my 14 years of racing (albeit on dirt/gravel mostly with some tarmac) Rosberg would have ended up all 4 wheels off the track without going full lock, he reacted and was not really trying to turn into the corner until a collision was already happening. This I do not think was malicious but an error in judgement by Rosberg.
But watch his deceleration rate was saving the turn in. Remember it's a very slow corner (about 60-70 degrees) so you can take pretty sharp angles at slow speeds.
So... Rosberg was going to do this?

No. look at his hands:

OK, I drive a lot on the track (not racing, just track days in a Caterham) and can feel when a car is understeering easily, I can even feel when its nearing the edge of adhesion. But I certainly cant tell from a camera view when a car is not yet understeering but may at some point in the future. Credit if you can, but you cant really ask others to rely on that intuition.
All we can really go on is the evidence from the oboards we can see and that shows there was no understeer and that when he did turn, the car turned fine.
The video shows me that his lock vis-a-vis turn in angle was giving smaller returns than is ideal, if you look at his trajectory. His deceleration would have caused the tyres to grip a half second later. There is an extreme visual example of understeer on YouTube which I'll try to find for you.
Based on this gif, it seems Hamilton's car was about 1,5m ahead of Rosbergs car.
When Hamilton start to take the corner, Rosberg still drive straight, so since that point he cant do anything to avoid the crash.
When Hamilton start to turn his steering wheel, it was an "alea iacta est" situation.
Yes he was still straight, but he was decelerating. The reason he couldn't avoid the crash is because Hamilton turned into him before Rosberg was required or ready to do so.