I don't think it's fair to suggest that such advice is stupid. Yes, it's easy to find examples where some muscle groups are trained daily with no ill effect. Calves, forearms, abs, etc are used in so many movements that it's likely they get used almost every day. Also, given the success of the Bulgarian Method, more people are training major movements daily. Olympic athletes do this as a matter of course. The military often repeats exercises like pushups and chin ups daily or even more often. The downside is that these groups often walk the edge between performance and injury. The general rule still holds. In most cases, taking a day of between working out the same body parts is a good idea.
But I think it's missing the point that the body, to some extent, works as a unit, in a systemic manner. The only thing that varies is which part of the system works in a dynamic manner, takes the majority of the stress, etc, not which part is active at all.
No bodypart ever works in isolation.
That doesnt just apply to calves and abs, but the entirity of the core, for instance, which is active almost no matter what movement you're engaging in, and other muscles are not necessarily "cut from a different cloth".
The planning of recovery is as important, but I just think the guideline should be to balance emphasizing a body part with high volume/intensity with recovery time, not to recover 48 hours whenever you engage any body part to any extrent regardless of volume, which is paranoid.