Earlier quoted context omitted.
So do identical twins count for one person?
Identical twins don't have the same DNA. Random link of Google: http://www.nytimes.com/2008/03/11/health/11real.html
Of course they are not, but for 99.6% of humanity the rule that your DNA is (very) unique holds true, and for identical twins even if their DNA is even more similar it is not 100% the same.
Clones (which do not exist (yet, or at least, human clones)) are the other exception.