Bias. What's the bias? Refs don't like Oilers? Canadian Teams? Orange and Blue?
I have reffed for 20 years. I have looked across the ice and seen a partner and said...awesome this guy is good. Others "Oh crap, long night." Call quality can be based on the quality of the refs.
The other part is each referee has a threshold and standard for their calls. I am sure with a percentage of the refs, they catch Hill's foot stick out. Others would have called Kane for a rough for falling on Hill.
There is no bias other than the perceptions of fans that think the stripes is out to screw them.