Questions about Hinnant's stack allocator

I've been using Howard Hinnant's stack allocator and it works like a charm, but some details of the implementation are a little unclear to me.

1. Why are global operators new and delete used? The allocate() and deallocate() member functions use ::operator new and ::operator delete respectively. Similarly, the member function construct() uses the global placement new. Why not allow for any user-defined global or class-specific overloads?
2. Why is alignment set to hard-coded 16 bytes instead of std::alignment_of<T>?
3. Why do the constructors and max_size have a throw() exception specification? Isn't this discouraged (see e.g. More Effective C++ Item 14.)? Is it really necessary to terminate and abort when an exception occurs in the allocator? Does this change with the new C++11 noexcept keyword?
4. The construct() member function would be an ideal candidate for perfect forwarding (to the constructor that is being called). Is this the way to write C++11 conformant allocators?
5. What other changes are necessary to make the current code C++11 conformant?