Good point BW
The thing is being born an atheist decreases the chance of being a believer, and being born into a believer environment increases this.
As an example take some nations in the OT who were there at the time of Israelites. For some reason they were unbelievers and hated God - or just did not obey Him, maybe simply because they never had the chance of knowing the 10 Commandments, or because their ancestors decided to be against God and hence they grew in bad environment.
Consider e.g. Islam people or other religion. Many religions believe "if you don't believe in my god you'll burn in hell". Now if you were born in islam and believe this on what ground should you convert? Just because there is 1 right religion does not mean automatically that everyone should go to it - other religions also have their reasons and can justify why the're the "right" religions.
Leaving this point aside, let's say you're an atheist or strong disbeliever and God grants you to change - e.g. Rich Deem who founded the G&S website!
So yes things happen. But if we take some statistics then I'd say those who live in families with strong and correct christian tradition have a greater chance of being saved than those born to the opposites. Exceptions happen; St Paul is a good example of someone who persecuted christians and then became a saint. However, Therese of Lisieux was born into a good family and although she is the only considered as saint, it looks like the entire family were a bunch of good people who liked God and got saved. Now if they decided to have 150 more children it may have happened that they'd all been saved, and if some evil family decided so and taught them to be evil and so they'd be like that.
Now no-one can choose where one is born, and hence cannot choose his own predisposition...
Now again - if JC is the only way to salvation, and someone is a strong believer in a different religion does it mean he cannot be saved?
"Love is only possible if a choice of either love or rejecting the love is given." One of the most true things id ever heard, not so long ago.
-MMS-
But yeah then free will comes into this. But predisposition etc play a role. Imagine yes you are lucky to be a nice person and live in Canada. Now imagine you lived somewhere near bad people or disbelievers so maybe you would be like that and then who is to blame? Exactly my point on some different topic but I'm just exhausted on going into details with this here 
Being born in nice environment and with nice genes increases the chance of being saved I'd say and being unlucky like never hearing about Christ and being "evil by nature" would decrease this I'd say so one needs to do more to have faith - but it's not works based this is another argument... anyway doesn't relate to war any more does it? 
But then there is a lot of speculation and what it means if JC is the only way into salvation.