Steven Riddle has an interesting post on the population of hell, suggesting that the kindler/gentler theology of the moderns might be a development of doctrine, and he may be right. I'm no expert, but it seems that while God doesn't change, our perception of Him is certainly a moving target. From least inclusive to most inclusive is the pattern of salvation history - from Adam & Eve to a family (Noah) to a tribe (Abraham) to the twelve tribes (Israel) to the Davidic kingdom to "here comes everybody" (i.e. the Gentiles). On the other hand, the last book in the New Testament certainly doesn't give me the "warm-fuzzies". There is immense spiritual warfare depicted, with high stakes.
Development is a tricky thing which is why I'm glad I don't have to decide what is and what isn't. Many non-Catholics, for example, think that the lack of disciplinary requirements in their churches (such as days of fast and abstinence and days of obligation) are "development" given that the New Testament expired many of the OT requirements and regulations. And in making sacraments mere symbols, they sacralize everything, they invoke a ubiquitnessness that denies the especial Presence. Some wrongly see that as development given the biblical trend. God was so inaccessible in the OT Holy of Holies that only the high priest could be there (extremely hierarchical), but that segued to the NT practice of all the faithful receiving Him and some project (too far) that Jesus intended a completely flat, horizontal Church. It is too easy to see the trend and follow it to (what you believe) is the logical conclusion. I've certainly been guilty of making this error in the stock market.
Part of the difficulty is that we are in a phase of Church history that is completed and yet not finished. In other words, although we are in the final days (meaning post-Pentecost) we still see through the glass darkly. The Church has recognized the glass is dark on this subject and has not weighed in on how many are saved. Reading theologians, on this subject, seems akin to reading tea leaves.
I just saw a documentary on angels on the History Channel, and they interviewed a man who had no interest in God who suffered an injury (lacerated intestine) that went untreated for 10 hours. 90% of the time it leads to death, and he had the classic near/after death experience - he looked over his dead body, etc...And he was given a choice to pray to God, which he did, and he lived and became a minister. He was utterly changed by his experience, something that a pyschologist says doesn't happen after dreams or hallucinations.
This is admittedly anecdotal, but if true here was a guy given another chance presumably after he died or at least in the second before death. That would certainly lead one to believe that hell would be less populated than one might think, given that if that man were given that chance, why wouldn't everyone? Alicia rightly says that those may still choose wrongly, but what amazes me about that is that it goes so directly against their self-interest. Who would choose death over life? You say that the drug addict does (or the sinner for that matter), but he does because he perceives a short term 'good'. There would seemingly be no short term good to choosing hell at the moment of death, would there? Perhaps only pride...which I suppose that is one reason it's the greatest sin.
Ultimately, the answer is unknowable on this side of the divide but that doesn't stop us from pure speculation.