I think you misread the point GP is making he is suggesting that because identical twins have the same DNA (more so than other people says the article linked) according to my logic they must be the same person, whereas it is obvious they are not.

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.

Clones won't have identical DNA for the same reason that twins don't.

You mean because of copy errors ?

I think they are referring to epigenetic changes (silencing/methylation). At the genetic level, they should have identical DNA if they arose firm the same egg/sperm combo.

Those are epigenetics ( http://en.wikipedia.org/wiki/Epigenetics ) differeces. DNA sequence is identical in identical twins.

True, but not every cell in your body has the same DNA either. Mutations happen with every cell replication.

not with every cell replication. that would certainly be pathological!