Average and Standard Deviation in .NET?

Question

Why aren't there arithmetic mean (average) and standard deviation/ pop std dev methods built into the framework?
The only references I've found say that there are some overloads for standard deviation in System.Data.Objects.EntityFunctions, but (even though I added the reference to system.Data.Entity), there is no EntityFunctions class in System.Data.Objects.
These are such standard, canonical functions that it seems obvious they should be in System.Math, or at least implemented as extension methods to IEnumerable.  Is this just an exercise to make sure all .NET programmers can do something this simple themselves? :D