Well, technically this is not true. What is true is that SCOTUS has, through the doctrine of incorporation, incorporated most of the BoR against the states by way of the Due Process Clause of the 14th Amendment. I'm quite happy that they did, although it was, and still is, a bit of a legal stretch. And not all of the amendments, as someone else said, have been incorporated. The 2nd likely will after McDonald v. Chicago. Other rights, such as the right to trial by jury in civil cases over $20, from the 7th Amendment, has also not been incorporated.
Oh, and interestingly, it is pretty widely assumed that the Privileges and Immunities clause of the 14th Amendment was meant to be used as a tool of incorporation, but SCOTUS gutted this in the Slaughterhouse Cases, so that the clause has no power.