The New Yorker uses "insure" for both meanings, and it trips me up every time.

Holy mackerel, you're right:

https://www.google.com/#q=site:newyorker.com+insure

At first I thought, "Well, but the New Yorker does have a few quirks" - but the analogous search for the NYT shows that they do it too.

I always assumed "insure" for "ensure" was a sign of illiteracy. What's that thing called in psychology where the brain edits out incongruent things and just doesn't see them? I must have been doing that with "insure" for years.