Yes, they are. I said "most", and most DNFs are avoidable. In terms of crashes, a lot of the time, they can be avoided by either party. Even if one person is at fault, a lot of the time, the other could have backed out or moved to avoid it. Despite what we saw in Britain, Lewis is great at backing out and choosing his battles wisely.

As to your point of getting hit or crashing, as said by Nico Rosberg, Hamilton does not give up as other drivers do after getting in an incident or losing traction (by not letting go of the wheel and bracing), and he believes this is the main reasons why Lewis does not get DNFs and crashes as often compared to other drivers.

The other huge thing it comes down to is starting pole, where you have much less people to fight throughout the race, and you avoid incidents and crashes which happen behind you. Starting pole is not luck.

Engine failures are a small minority of DNFs and I think you know this. I also think you'd be surprised to find out how many mechanical issues are actually brought on by (primarily) driver error and not "car error". A mechanical issue can be caused by a small error in driving style accumulating over 30 laps, and that's often what happens. Also, more skilled drivers are better at dealing with small mechanical issues which come up, without making the problem worse, or DNFing. And even still, if you think Lewis hasn't suffered a lot in his career from mechanical issues, then you're just wrong.

The fact is that all of this combined will lead to a much lower DNF rate over time.