I would also say that you shouldn't worry. As SomeoneSomewhere already mentioned, this storage capacity difference comes from the different measurement standards used.
More on this topic: http://products.wdc.com/support/kb.ashx?id=jWZqTg
My tablet says it has 16Gb of memory but in settings it shows only 14.(bla bla bla) Gb thats normal because producing hard drives they are not precise figures are rounded (Im using Google Translate because im latvian )