Wage slavery is generally means someone who is so beholden on his day-to-day earnings as someone's employee, that he is in little better condition than a slave. The was a term originally used by Southerner's in the United States to justify their practice of slavery.
In general it implies a wage set at a point were there is no surplus beyond your day-to-day needs. With the United States having had a negative savings rate for some time now there is an argument to be made that we have been in this position for some time.
Of course the counter argument is that we did not to buy all those new houses, SUVs, and wide screen TVs either.
One would like to look back to a better past when people lived in their rural communities on their parcel of land and did not have these worries. They ate what they produced, and only needed a tiny surplus for taxes and a few items they needed.
Unfortunately, this picture of blissful agricultural communities would probably only apply to farming communities with excess land at hand. After the collapse of Rome with the Barbarian invasions, there was a lot of excess land for the medieval system to slowly grow into. After the Black Death in Europe there was plenty of land for a while. The American Colonists pushing across the west also had potentially plentiful land: though not always without a fight.
But these were not always the case. As Dominic Crossan points out in his books about the time of Jesus in the Holly Land, many laborers did work on other peoples land. In fact the word that is translated as "Carpenter" in the bible, could just as well be translated as "Laborer." And even if Joseph had been a skilled Craftsman, he still would have ranked below the people who held their own land and could live of its fruits. It is likely this reality that Jesus was referring to the fact that we would always have the poor among us.