Ruin Explorer
Legend
"The system" has to account for this?
Isn't that what a DM is for?
Not to do it alone and unaided, no.
The system, eeyore, the CL system, the encounter-building system. WotC have talked about it quite a bit, and it's in evidence in the previews (and to a lesser extent, in the playtests).
WotC have SPECIFICALLY STATED that they intend for magic items to be possible to account for when building encounters, and that they will have guidelines for that. WotC. Not me. WotC.
WotC have also stated that they intend the encounter building system to be robust and reliable, something that 3E's system was absolutely not, and that 4E's system was. So they have a clear goal - to build a robust, reliable system that allows you account for magic items in a way that doesn't make the system less robust or reliable.
The DM is there to design the encounters and so on, but frankly, most DMs need or at least can benefit from help/advice on designing appropriate encounters, and having some stuff called out. This is very evident from years of play, being on both sides of the table. The unaided style of play from 2E lead to a lot of misjudged encounters, and worse, a lot of scrutinizing monsters for things that could be problematic, which took a lot of time and effort, and which it's quite possible for WotC to do FOR us. And they are, or claim to be. And that's a good thing, because at worst, you can ignore this system. It doesn't PRESCRIBE what monsters you can use, it merely suggests and/or shows you the likely consequences.
(Of course, as discussed, this kind of system can be a bad thing - but not because it's prescriptive - there are no gaming police - but rather because it's actively misleading, as the CR system of 3E was, or judging solely or primarily by HD was in 2E).