Time for a history lesson:
FACT: The printing press was not invented until the mid-fifteenth century. Prior to this, all Bibles had to be transcribed by hand, this was an incredibly time consuming process and as a result Bibles were extremely expensive and far beyond the reach of the average person. Keep in mind in these days, most peasants actually rented farmland from noblemen and their was no available credit. It was absolutely impossible for them to purchase a Bible.
FACT: Because books were so rare, very few people knew how to read and write and schools were really only for the wealthy because the poor needed everyone working. Any learning by the poor was generally confined to math for use in trade/bartering. So, even if the average person came across a Bible, they would be unable to read it.
So, please explain to us WHY God would construct a plan of Salvation knowing that it would be impossible for all except the most wealthy to follow for at least fifteen centuries. Do you believe that God is that cruel and mocking?
Not only did "sola scriptura" not exist prior to Luther, IT WAS TOTALLY IMPOSSIBLE.
Now don't go ruining this by bringing facts into the equation. Dude, did you not read the article....facts aren't the issue here.