param2 = param1

[Luís.Marques]

Is there a reason why template parameters can default to other 
template parameters, but not regular parameters? For instance:

    // OK
    int foo(int x, int y = x)()
    {
        return x*y;
    }
    // Not OK
    int foo(int x, int y = x)
    {
        return x*y;
    }

When I noticed this it seemed arbitrary, but maybe there's a 
reason?