Poll aggregation vs poll averaging
Real Clear Politics averages polls and posts the results. They do not aggregate them in a propitiatory algorithm and try to make a single poll of multiple polls. Nate Silver and Simon Jackman both scrutinize the poll's data and weigh them according to the poll's history, house lean (left or right), sample size, and may many other proprietary inputs.
Further Jackman (and Franklin er al) at Pollster.com precedes Nate Silver by a year.