We do not have a storage calculator because we believe providing accurate numbers (even as close as + or - 30%) is generally infeasible.
There is definitely differences in bandwidth across models. That's something that is rarely taken into account.
The bigger, impossible to solve, problem are differences across scenes, even for the same model. Even something as simple as zooming a camera in or out can double (or half) the bandwidth needed depending on what is being captured. See Advanced Camera Bandwidth Test Results for many examples of this.
Essentially, there's no abstract way to accurately determine the bitrate of a camera. Knowing the model and the general scene definitely helps but there's still real risk.
There's no storage calculator that I have seen that attempts this across multiple manufacturers. Axis does the best for their own cameras only (obviously) - see the Axis Design Tool.
In general, I recommend measuring the bit rate of your own cameras in your scenes. This takes some time but will provide far better results.
For more, see: How to Calculate Surveillance Storage / Bandwidth
Also, to get a feel about how vendor's trick / game this, see: Guaranteed Video Storage Calculation? Iomnis
Thanks for the detailed response John. Storage is an area in our industry where there is an element of art and science. I would agree that the calculators I've used in the past aren't any more accurate than +- 30%.