Google is not a tier 1 provider, there are only 6 of them.

Putting traffic into a tier 1 network costs, taking it pays.

A massive surge from Googles hardware onto the tier 1 networks will be very, very expensive.

Last time it came up was as the BitTorrent protocol started blowing up ISPs that couldn't pay the bills.

Google peers with many national and regional ISPs at exchange points. I don't know the exact numbers, but I'm guessing a fairly significant portion of their traffic does not go over traditional "tier 1" networks and rather is handed off directly to ISPs.