>Surely google.com is as 'surprising' to the user as any other page.

The metric isn't how surprising it is, but how potentially malicious it is. The entire point of the redirect is so the user can make a conscious decision not to visit a potentially-malicious page.

Google.com and Youtube.com, operated by the same people who made the docs tool, make the entirely-fair assumption that neither contain malware.

That being said, I also think it's the wrong argument to make. It makes very little sense that an exported document needs these interstitials. It would make more sense if it applied them to hosted Google Docs, but not things that are self-hosted by an end-user.