Technology is very good at creating value, but not very good at creating jobs. All 72 tech companies in the S&P 500 combined employ about 2.3m people [1], whereas just Wal-mart employes about 2.1m people. Those numbers are worldwide employment, but for reference, the US had 15m unemployed in November.
Even the breakout, unimaginable success that is Google only employs about 28,000 people. And I'm sure that for every hire Google has made, they've displaced many more people that used to depend on print advertising. (To be clear, I'm not saying that technology is net bad for the economy. Technology creates a lot of value for the individuals that work and invest in it, and for the economy as a whole. However, technology is not a massive creator of jobs.)
So unless startups become a multiple of the size of the entire S&P 500 technology sector, they're not going to make a noticeable dent on unemployment.
[1] I compiled a spreadsheet (https://spreadsheets.google.com/ccc?key=0AqpDDf0Sr4EXdDJMZEt...) based on information available on Wikipedia[2] and through Google searches
[2] http://en.wikipedia.org/wiki/List_of_S%26P_500_companies and individual company pages