Despite the fact that this is constantly stated, it is just not true.
If that were the case, how would most people have heard God speak prior to the printing press?
You may think it isn't true, but the bible is supposed to build up, encourage, comfort and edify Christians. If you mean during the more modern times before the printing press then people had missionaries and teachers to tell them about what was written in the bible, although not many would understand it during for example the time of the Roman Catholic church where the bible was just written in Latin. Now this is why Martin Luther and others came into the picture, to translate the bible into more languages so that people could also learn to read it in a language they understood.
Virtually nobody could read in the OT or NT period until relatively recent times. Were they excluded from God's intentions?
No. In the ancient times God spoke more in an direct way to those who loved Him and found favour in His sight, as well as they had the prophets who told them what God had in mind. Although don't forget that as time went by they would read in the main jewish laws as well as other Scripture scrolls, Jesus even read in a scroll which was written from Isaiah. During the NT they had Jesus and the disciples(not only those who were picked out by Jesus).
How do non believers, or those in non Christian countries hear God speak, if they first need bibles?
They will most likely hear it from missionaries, or from other Christians who are also living in their country. If they never have heard anything about God before how can they then call out for Him?
The reason that few people receive words directly from the Lord is because they are constantly being told that he speaks mainly through the scriptures!
How do we know whether God is speaking personally to us from scripture, rather than just to the characters in that book? We cannot just grab hold of some biblical injunction and apply it to ourselves or to others without some other guidance, otherwise we might find drastic results.
ie. We don't see too many Christians making use of this injunction do we, despite it being the word of the Lord in scripture?
Matt5v 28But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. 29If your right eye causes you to stumble, gouge it out and throw it away. It is better for you to lose one part of your body than for your whole body to be thrown into hell. 30And if your right hand causes you to stumble, cut it off and throw it away. It is better for you to lose one part of your body than for your whole body to go into hell.
To understand what the Lord might be saying to you through scripture requires both common sense and discernment.
To understand what the Lord might be saying to you through a strange experience also requires common sense and discernment.