How would you call the constructor? When you use interfaces, you normally pass an instance of the interface around (or rather, a reference). Also bear in mind that if one class implements an interface, a derived class inherits that interface, but may not have the same set of constructors.
Now, I can see the use of what I call static interfaces for specifying constructors and other essentially static members for use in generic methods. See my blog post on the idea for more information.
