40%-50% of people in the Earth were owned bitcoin by 2020. Because most of the people were still scared to scammed, they always thinking that online or digital transaction were scam especially to the old one. But I'm still hoping that most of the people in the Earth were accept the value of bitcoin.
I would like to disagree with your statement that by the year 2020 the number of bitcoin users out of the worlds total population will be that of 5 to 10% only. Saying that there will be 40% to 50% is very high and is very impossible to occur at that time of the year. But if we talk about 20 to 50 years from now possibly your computation may come true.
Nothing is impossible with the internet when it comes to propagation, advertisement and adoption. Internet advertisement can reach almost all parts of the world. Every single day, new people come in to bitcoin economy, so it would be possible that the growth of adoption would be exponential since each person that is into Bitcoin can influence two or more people to join him with his venture to bitcoin industry.
But the greatest difference is that those things that propagate over the internet dont need any kind of investment from the users, if you want to benefit from bitcoin then you need to fork some money and that is not as easy, people love free stuff that is why you have things like youtube and facebook.