I don't think it's absurd at all. As other commenters have mentioned, seeing the coupon code box and not having a coupon gives me (personally) a feeling of remorse before I've even bought what I was shopping for. This should concern you, as a merchant, because ideally you'd like your users to associate good feelings with shopping on your site.

Beyond the "feelings" aspect, I suspect that, as is argued in the article, the coupon code box does lead in some cases to cart abandonment. I've certainly seen the box, gone on a hunt for a coupon, and ended up buying the same item at a different vendor during my hunt many times before.

Personally, I think the best solution for this is either special urls (i.e. www.shop.com/summercoupon), or a "Where did you hear about us" box, which could double as a coupon box, and just an interesting way to gather data about your users. Sure, you'd probably get a lot of garbage, and you'd have to put more effort into parsing the values, but, in addition to not alienating users, you might find some valuable insights as well.

[edited for grammar]