Most, not all, of the snow removal / maintenance folks I deal with decided to go with a yearly fee this winter and are perfectly happy. I have discussions with my clients in Aug/Sept and discuss whether to play the odds of a yearly fee or a per storm contract. This year most decided to roll the dice with a yearly fee option, and are happy, so far with the winter tenor.
As for the litigation side of things, I deal with many dozens of those case every year. Juries are quite open to siding with the snow removal guys, if they can show a well-documented work procedure. I always recommend an after clean-up brief video, or at least pictures with a logbook of times of cleaning and treatment applications. Most juries understand the nature of Northeast winters and fully understand it is impossible to clean surfaces to perfection; especially when dealing with parking lots / driveways and walkways that were being used during an event. The key is to document, take pics and/or video each storm. It might sound tedious, but it can make all the difference when it comes to lawsuits.