Google Online Sales/Operations (OSO) is notorious for hiring smart, super ambitious 20-somethings from top schools and giving them temp jobs in customer service with the carrot of the possibility of a full time position maybe. Not sure how much of that 10,000 is OSO, but I have to believe it's quite a bit.

Google is an engineer-first culture, so it would surprise and amaze me if there were that many software engineer contractors.