I wasn't aware of it, but I think it still makes sense. [`TouchSource.vacuumTouches_()`](https://github.com/tsauerwein/ol3/blob/pointerevents/src/ol/pointer/touchsource.js#L256) issues `pointercancel` events, when there was no `touchend` for a `touchstart`. 
Now, let's say a first `touchstart` is registered on `pointerEventHandler_`. The `documentPointerEventHandler_` is set up. But `documentPointerEventHandler_` doesn't know about the first `touchstart`. If there is no `touchend` for the `touchstart`, we can only receive a `touchcancel` from `pointerEventHandler_`, because it is only registered there.

I hope this makes sense.