A FAQ is, if the Gospel is the only way to God, then why do some people have more access to it than others? Is this fair?
Let me lead off with a very important and powerful passage, Romans 1:18-23.
"For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth. For what can be known about God is plain to them, because God has shown it to them. For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse. For although they knew God, they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened. Claiming to be wise, they became fools, and exchanged the glory of the immortal God for images resembling mortal man and birds and animals and creeping things."
Really, that is the bottom line. God makes it fair, and we can trust this. However, at the risk of over-expounding, I have some additional comments about the possible ways that God does this.
Possibilities(Edit)
Obvious(Edit)
I think the simplest interpretation of the Scripture above is that God makes Himself evident to all people inherently. We automatically know all that we need to know about Him, and it is our sin that clouds the knowledge out. I believe the wonderment of nature falls into this category. In fact, all of creation praises God (Psalm 69:34, etc.). How can a person look around and not see the loving hands of God all about us?
The Law and the Prophets(Edit)
Observe Luke 16:19-31. Verse 31 says, "If they do not hear Moses and the Prophets, neither will they be convinced if someone should rise from the dead." Even if a person does not have access to the written Law, they have the Law already in their hearts. Every person is also guilty of violating that law---and knows so. This guilt makes it clear that we are separated from God, which should cause a righteous panic in each soul. This drives us to find a solution, a way to clean off the black spots from our heart. That solution is Christ alone. If we do not heed our conscience's cry, then we distance ourselves from the chance to find the Savior.
Incremental Leading(Edit)
Another possibility is that God leads a person to Himself step by step, as they accept the simpler truths and graduate on to deeper truths. For example, imagine a person was born in a polytheistic culture, but feels in their heart that there is only one God. If they are a good steward of this truth, perhaps God will reveal more and more, leading them out of the swamp of lies and into the truth of the Gospel. James 4:8 says, "Draw near to God, and he will draw near to you."
Tribal Curse(Edit)
Something else to consider is that, according to Biblical history, people started out with knowledge of God (starting with Adam, then again with Noah). Noah had some sons that rebelled against God and departed from the tribe---and the faith. Each generation has the choice to stay with the beliefs of their parents or to splinter off. When a generation does this, it handicaps subsequent generations. The sins of the fathers are borne by the children (as in Deuteronomy 5:9).
Mercy Silence(Edit)
Now consider God's foreknowledge of man's actions + this verse, Luke 12:48: "Everyone to whom much was given, of him much will be required, and from him to whom they entrusted much, they will demand the more." If God knows a person will reject his every courting, then He is only heaping further judgement on that person by further revealing the message of His Son's sacrifice. Now, recall that God knows us from the womb (Jeremiah 1:5). Perhaps the souls that are born in Godless nations are exactly the ones that would reject Him in any nation? In this way, God has mercy by silencing the preachers relative to these people.
Direct Appearance(Edit)
Don't forget that God can directly intervene in a person's life. Look at what happened with Paul (Acts 9:3-9), or this brother: http://www.youtube.com/watch?v=NvvClFSMIzA . I have no idea why He does this for some but not for others. What I do know is that it is a possibility.
Stop Time(Edit)
(This one is pure conjecture.) Another option is that, in the instant before a person dies, God could stop time for that person and send an angel to communicate whatever it was that the person did not get a chance to hear. We cannot have a record of this because all of the people it could have happened to are now dead---but the opposite is also true: we cannot know that it is not happening. I bring the possibility up to remind that our sovereign God can solve any puzzle, can right any wrong, and can accomplish any feat. We are not in a position to doubt His ways because they are infinitely higher than our ways.
Conclusion(Edit)
I once asked a Youth Pastor about this issue. He laughed (non-derisively) and said, "That's God's business!" This is the truest answer. We really do not know how God deals with each person, but it is revealed that God is just. We can rest assured that whatever He is doing, He is doing what is fair, loving, and complete.
Thank you for reading; be blessed.