score:21
The NIV has some "missing" verses because it is based on different manuscripts than, say, the King James version.
For some background, we don't have manuscripts of the original writings of the New Testament. We have copies of them, and as with text that is copied manually, there is room for copyist error, or for people to add or remove things - purposely or inadvertently. Note that copyist errors don't affect the doctrine of inspiration, inerrancy, or infallibility of the Word. And even though there are slight changes, it's still reliable for doctrine.
The verses that the NIV "removes" are simply not in the manuscripts used for translating it.
There's more detail available all over the web. This is one such page.