Nothing is inpenetrable--read "the art of deception" by Kevin Mitnick
The only unhackable system is powered off, locked in a crate, and sunk in the ocean. All security systems, whether electronic or otherwise, are always in a tradeoff with ease of use, effort, and money.
Bluetooth is such a great technology - I am glad this weakness was found before it is in every house, car, and tennis shoe.