The kind of person who describe isn't an ordinary person. There are much more Mr Zhangs than Mr Smiths. Half of India's population has no bank accounts. http://blogs.wsj.com/indiarealtime/2012/11/01/why-few-indians-have-bank-accounts/

There are many people in this world who have cell phones but no bank accounts. In ten years they probably have smart phones.

Those people might want to do low-wage online work and get payed despite having no bankaccount.

A lot of bitcoins economy will however still be illegal payments. Some third world towns that make their money through the drug trade
might switch to using bitcoins for their regular transactions as well.