Well, this goes back to the conversation I'm having with [MENTION=37579]Jester Canuck[/MENTION].
If the GM doesn't adjust difficulties on his/her side of things, then having a +1 weapon or armour just makes encounters easier, which (typically) makes them less interesting, which isn't really a bonus.
And if the GM does adjust difficulties (via upping the budget for encounters and/or adventures) then the magic item isn't really a bonus anymore (except in story terms), as the GM-side maths has been adjusted to accommodate it.
I think the point here is that it's not automatic. Magic items will make you noticably stronger against foes in the game, but the edition will contain *advice* for GMs in balancing adventure challenge based upon the number of magic items used.
I for one will be judging that advice based upon how much it enables the GM to choose an appropriate challenge level, rather than automatically compensating.
It's important that the players can be challenged by the situations they find themselves in, but this should be story-based (in my games, at least).
As an example... I'd want magic items to affect ths difficulty of plot-specific threats (those where an in-game entity is responding to the players' actions and skills) while not altering wandering monsters at all.