A good illustration of why the single number for the EPA range estimate of any electric vehicle is not really that useful. Electric vehicles should come with a chart like that so people could really plan a route. Maybe some information for elevation change as well.
Note that some points on that chart are less than half the EPA range number, and it doesn't even include really cold weather.
Is John Q Public really going to sort through all that and understand it?
As an engineer, I might, and I'm sure there's some interesting details to be found.
However, I think the current approach is probably the best for the general public - a single number that's vaguely representative of "typical" conditions - and consistently comparable between different cars.
The other option I could see would be to have a set sample route - NYC to Boston, say - and show how far the car would get/how much energy it would use if the driver drove it in the typical fashion on a typical spring/summer/fall/winter day. That's a completely realistic example that could still be expressed with only a couple numbers and be easily comparable between cars. The downside is it may or may not bear any resemblance to the typical usage of the particular buyer.