I just wanted to add that the term "Ahl AlKitaab" is only addressed to 'People of Musa(AS)' and 'People of Eisa(AS), if I am not mistaken, inshaAllah. And 4:159 used the same term.
The term "alkitaab" does not translate into "book" nor "scripture". It's a collection of subjects united by the same theme. If you are familiar with the books of fiqh, you will find that they are divided, not in chapters, but in "kitaabs" and hence "kitaab ul-sariqaat"...etc = book of theft or Cahpter on theft. Same thing as for ancient egyptian writtings and the famous "book of Death". All messengers were given "the book", including Muhammad.كَانَ النَّاسُ أُمَّةً وَاحِدَةً فَبَعَثَ اللَّـهُ النَّبِيِّينَ مُبَشِّرِينَ وَمُنذِرِينَ وَأَنزَلَ مَعَهُمُ الْكِتَابَ بِالْحَقِّ لِيَحْكُمَ بَيْنَ النَّاسِ فِيمَا اخْتَلَفُوا فِيهِ Translation:
Mankind was one single nation, and Allah sent Messengers with glad tidings and warnings; and with them He sent the Book in truth, to judge between people in matters wherein they differed; ....
The one thing they were all given are the universal laws: "the Straight Path" (chapter 6 verses 151-153) to Muhammad, and the Ten Commandments to Moses, called also "alkitaab".
Therefore, the people of "the book" are the people aware of the universal laws and abiding by them.
Please remember that words such as Judaism and Christianity or any title to whatever religion apart from peacefulness (islam in Arabic) do not exist in the qur'aan.