The article discusses the environmental impact of producing and dustributing the toilet paper, but not the impact of manufacturing, installing and upkeeping the bidets. By my totally uninformed guesstimate, it would take a lot of toilet paper saved to balance the impact of one bidet installation. The article argues that bidets are better for the environment; I would need to see an estimation of how the bidet installation balances against toilet paper usage to be convinced by this.
Umm, using a bidet doesn't exclude at all using toilet paper. It's an "enhancement" to the cleaning process. I often see this misunderstanding in places where bidets aren't the norm (or the law). So, a play on words on the Scientific American article's title would be "Wipe AND wash" and not "Wipe or wash?".