I'm one of those just out of school Googlers and while I obviously have no experience at MSFT I'll tell you why I don't see myself becoming bored at Google.

Google has a best-in-class (top 5?) product in pretty much every category of software. In 10 years a Googler could work on Drive, Android, G+, Gmail, Fiber, and Maps. While working on those things he/she will be exposed to an unparalleled developer infrastructure (Google's internal tools are rigid, but insanely well engineered). So why leave for another company when I could just change managers to work in pretty much any field on software? The only reason to jump ship would be toxic culture or money, and right now Google is at the top of the heap in both culture and pay.