The C++ reference clearly state that calling
elements can be accessed not only through iterators, but also using offsets on regular pointers to elements
One of the principles on which the conceptual idea of iterator is built, is as follows: as long as iterator remains non-aliased, dereferenceable and non-modified, it should refer to the same entity. In other words, dereferencing the same iterator multiple times should yield the same value. Algorithms that use iterators may rely on that.
What you proposing would result in an iterator that would "magically" change the value it refers to even though the iterator itself remains unchanged. This is not acceptable within the conceptual idea of iterator.