Li Shenron
Legend
I still think they could clarify just a bit. For a new DM this could be (and is) confusing. They've done quite a bit to streamline the rules, for the better I think, but in their effort to smooth things out they've gone a little too far in some areas. But I do appreciate the input.
Clarifying with examples in the DMG would be good.
Precise rules however can be dangerously counterproductive for the inexperienced DM. There are way too many variables, when you add written rules it always opens up a couple of corner (or not-so-corner) cases it fails to represent properly, calling for more rules which open up more corner cases...
Just to quote the very basic case of a creature hiding in a specific place, as the party of PCs passes by... It would make all sense, as other suggested, to roll the check when the creature is within sight range. Indoor this is simpler than outdoor. However, if the first PC getting close enough (e.g. someone with darkvision) misses the check, do you let the party roll again when other PCs get close enough? Do you let each of them roll a separate check? Because if you do, this tremendously changes the overall probability of success. It will be very rare for a party of 4 not to spot an average hiding creature, the DC of which is probably designed (e.g. as a stealth check result) against a single perception check. Do you randomly choose one of them only to make the check, but then who and why? Do you "aggregate" everyone's perceptions on have a single check for the whole party?
I think they will probably add guidelines, but ultimately you have to just DM by intuition and experience. I don't think they want to write precise rules, because they would easily get out of hand and be worse for an inexperienced DM than having to adjudicate.