My understanding of scripture, is that a person is held accountable for the amount of knowledge he has acquired. If he grows up never having been exposed to the Gospel, how can he be held accountable? I know that some churches preach the "age of accountability." And Catholics believe in original sin, if memory serves me right.
You're really asking another question.
Why do we make the choice to choose Jesus or not? We usually choose Jesus based on reasons in the heart and then the arguments follow and not always before. Did our heart follow the amount of light that we are exposed to?
Even if they have not His gospel, the Holy Spirit comes along side people and if they follow or if they don't follow may answer the question on those who never heard the gospel.