I haven't done the maths, but I strongly suspect the number of celebraties dying would have to be absurd before it became statistically significant. They've all gotta die some time.
I think it's specifically who died in the early part of the year, along with the unexpectedness of it, that helped further this idea that 2016 has been exceptional. Similarly, when Steve Jobs and Dennis Ritchie died within a week of one another in 2011, it wasn't necessarily statistically improbable, but it was still quite a double whammy.