Why does Boyne end the book The Boy in the Striped Pajamas in the manner he does rather than two paragraphs sooner?

It is important to note that there is a difference in
Bruno's father putting together the pieces of the puzzle and discovering the probable
truth of his son's fate than Bruno's mother and sister, as in the movie.  The father was
the Nazi soldier in charge of the death camp and of putting the Jews to death.  It is a
stark constrast to his son's humanity and his ability to connect with the little Jewish
boy on the other side of the fence...the message here is that under our clothes, we are
all basically the same.

The last paragraphs do two things: 
they distance us from the story a bit with the "it happened a long time ago"
statement...a sort of effort to release tension and the reins of social responsibility
for the reader;  they also make us question the statement "it could never happen
again".  Of course, this sort of thing could happen again if we choose to close our eyes
and ignore the past.  The past can and will come back to haunt those who do not
understand and remember.  In any culture where two groups of people are warring, there
is the risk and threat of genocide.  Take a look around the world today...is it
happening in the Middle East?  In Africa?  Your answer must be "yes."  Boyne is
attemting to use the closing paragraphs as both a lesson and a warning.  We must be
vigilant.  We must not allow our neighbors to be oppressed, lest we also become
oppressed.  We must also guard against becoming oppressors.