I still suspect you can complete them a lot faster than you think yourself. I seem to recall spending ages completing games back then, but when I try again today it's over in the blink of an eye.
For example, I remember Kings Bounty(predecessor to Heroes of Might and Magic 1) being extremely long and difficult. It's not. The final boss is still a pain, but other than that I can complete most of it fairly fast nowadays. That goes for most old games, only a few RPGs are exceptions, such as the Baldurs Gate games. Even PS:T only takes a few hours now if you know how to solve the various quests.
I think it's because I'm less patient now. I used to spend hours just walking around, talking to people, watching the scenery, checking out stats on various items and so on. I never do that anymore, I jump into action as fast as possible and hack my way to the ending scene.
Take Monkey Island 3 as an example. How long does it take to complete it now, compared to the first time through it? I think I played that game every day for two weeks before completing it - now it takes me an afternoon. If a game as short as Monkey Island got released today, it would get butchered in the reviews for offering too little content.. yet we still call it a classic. I think our expectations today are not what they used to be, and that might be an explaination why we consider "old developers" better than todays'.. they are, in fact, the same bunch but in different companies, hehe.