I think that after Shoreham there are concerns about off airfield spectating.
By buying a ticket for an airshow you have accepted that there may be some increased risk by being there.
It is not clear that is the case for off airfield spectating and there is therefore a greater chance of a gaining a larger legal settlement in the event of a claim for compensation.
The effect of that would to be to increase insurance cover required by organisers- something I for one would not want to see.