Initializers

I'm very confused among different types of initializations:

zero-initialize:
    scalar: set to 0
    class/array: initialize recursively
    union: initialize first member
    reference: no-op

default-initialize:
    class: call default constructor
    array: initialize recursively
    reference: ill-formed
    others: no-op

value-initialize:
    class with user-provided constructor: call default constructor
    non-union class without user-provided constructor: zero-
initialise and call non-trivial constructor
    array: initialize recursively
    reference: ill-formed
    others: zero-initialize

implicitly-defined default constructor:
    default-initialize base classes and members recursively

When the direct initializer is (), the object is value-initialized but
consider the following:

#include <iostream>
struct A
{
    A()
    {
        std::cout << "test" << std::endl;
    }
    int x;
};

struct B
{
    // non-trivial implicit default constructor
    A a;
    int x;
};

A x; // x is zero-initialized and then default initialized so that x.x
== 0

int main()
{
    A *p = new A; // p->x is not determined.
    A *q = new A(); // q->x is also not determined?! A
standard caveat?!
    delete p;
    delete q;
    B *r = new B; // default-initialized recursively: s->x
and s->a.x are both indeterminate.
    B *s = new B(); // zero-initialized first: s->x and s->a.x
are both 0
}

Also, how does zero-initializing a reference make sense?