Why is it that christians think they have the truth? What makes it any different from the Jw? (bar for the glaring obvious doctrine differences)
Well, one can be a Christian and be very much like a JW (and I know some of this kind), or one can be very different. In my view, there are one of two basic ways of viewing things that most Christians have.
1) That God has always tried to reveal Himself to all peoples, and that people have understood Him imperfectly at different times, until He revealed Himself perfectly in His Son. All religions have prophecies that point to similar ideas about God because He has tried to speak to them and they have tried to seek Him. The human spirit is designed to seek certain symbolic ways of representing the divine, and, while God has placed limits on these to avoid us worshipping the representation instead of the reality, common religious rituals and symbolism can be understood by looking at the psychology of the human mind that God created in all of us.
2) That God only ever spoke to Moses, Jesus, St Paul and Martin Luther (etc). That every other religion are worshipping gods that are really different images of the devil. All religions have prophecies that point to similar ideas about God because the devil is so good at mimicking God to draw people away from Him. God has left this tiny number of witnesses in the world, and is content to let the devil control all of the other world religions, and to let him successfully deceive people who earnestly desire to serve God devoutly into devil worship so they get sent to hell.
BTS