Speed clearly was a factor but it comes down to two things for me: 1) That if a driver was paying proper attention to the road, they should have seen the bike, even travelling at speed. I understand that most people including myself sometime drive on "auto pilot" but that's no excuse for proper observation. 2) The car's actions because of this lack of observation mean that the biker would have had to take action to prevent a collision, be that breaking, swerving or otherwise.
None of that excuses the clearly excessive speed, but if the driver was paying the attention they should have then the accident wouldn't have happened. If the biker was travelling at a slower speed it may have still been a fatal accident, even at 60mph.
That's not to say the driver's actions were proven to be well below that of a careful and competent driver to reach a conviction, just that I would place more blame on the driver.