Mashable posted a followup a few days later saying that study was most likely a hoax: http://mashable.com/2011/08/03/ie-users-dumb-hoax/

I never saw that followup - Thank you for clarifying.

You don't have to call them stupid. The product is a book aimed at young children. Older people are more likely to be parents or grandparents. So those that are more likely to use IE are also more likely to be the target audience.

The book seems really cute, as well, and a clever idea. If I was older and had a kid, I might have even considered buying it.

If you know a kid you could buy it for them ;)

#1 sounds a little more plausible, otherwise this would probably be a more common occurrence.

Perhaps something about it appeals to grandparents.

One suggestion is that IE users are more likely to have been directly referred by word of mouth, and so more likely to buy