I doubt that spam "accounts for 90% of traffic on the internet". Maybe 90% of email traffic.

Makes you wonder about the Economist and its fact-checking department. Really, everyone who looked at that should have questioned it.

Oh, well:

http://torrentfreak.com/bittorrent-the-one-third-of-all-inte...

...realistically, I wouldn't be surprised if the bandwidth consumed by gmail's page views (html+javascript+css+images+etc) exceeds its backend email load.