As stated a moment ago, this is a newbie guide for rogues. They're not going to always have the best gear available. And they'll probably be running hard/elite content a lot, as that's what pugs do. They rush in, not following our n/n/n/s/h/e xp run formula. As someone who almost exclusively plays rogue-splash multiclass builds, I can assure you that dumping Wis, while not having level appropriate gear, will almost definitely NOT spot those traps on hard, and CERTAINLY not on elite.
As this was for new rogues, I strongly believe that dumping Wis on your first rogue is a big mistake. It doesn't take a ton of points to get it into a reasonable range, so I think it's a good idea.