MultivariateNormal, Categorical, etc. do not inherit from ExponentialFamily

I noticed that several exponential family distributions such as MultivariateNormal and Categorical do not inherit from the ExponentialFamily base class. Is there a reason for this?

On a side note, it would be very useful to make the natural_params property of the ExponentialFamily public. Several operations, e.g. the product of N densities (probabilistic sensor fusion), can then be trivially implemented for any/all distributions in this family.