What is important to note is that spoken words are only heard when they are spoken, written language lasts forever. Of course, now that we can record voices that is not entirely true anymore. However most of what we know about history is thanks to written language.
The reason why we know little to almost nothing about the stone age, is because people in that time couldn't read or write. When it comes tot he Romans, the Egyptians and Greek, we know a lot more, thanks to the stuff they wrote down. Of course, we must take the general consensus of the time into account and how people felt. King Superbus for example, the last king of Rome was kicked out of Rome and they swore never to allow a king again. He is depicted as an absolute tyrant, and one of the worst of the worst, but if he was really that bad, or even if he was bad at all, is a bit guessing work since all written text about him was written by his enemies (as far as I know), so a bit of propaganda could be there, so you can never tell if the stories are actually true, and what is true and what is a lie. But overall, a proper image of the Romans, their society, their religion and their political system is something we have a rather clear picture of thanks to written text.
Also when I say something to you and tell you to pass it on, your version of my story would already differ on some point and the more it's passed on the more different it becomes and eventually it may come to a point nothing of my original story remains. When you pass on written text this could never happen.
Of course, spoken language was there before written language existed and due to many people not being able to read/write (that everybody is required to be able to is only something of the relatively recent times) and history has been based on this too, and maybe even in a more important role altogether....
In the end it's like comparing grapes with melons...