Noone really expects to achieve a 50% increase but people tend to want to keep ahead of the price of groceries and not end up in living in a cardboard box as a minimum. The old three percent (as ggrowler has just indicated
) doesn't really cut it anymore.
Just compare (1992-2007) the dollars for teacher, nurse, bricklayer, pilot and house. Some would say we loose ground every year.
There is a "shortage", a shortage of people that can afford to live on 40-50k.