I read though the new magic item information from the DMG. The way it is presented, it seems to only reinforce the core definition of a magic action: "When you take the Magic action, you cast a spell that has a casting time of an action or use a feature/magic item that requires a Magic action to be activated."
I agree with ad_hock that some items require "the magic action to activate" and some don't (they have more specific rules)
"It usually takes a Magic action to activate a magic item. ... Certain items use the following rules for their activation."
(and there it details the specific rules for "spells cast from items")
"Some magic items allow the user to cast a spell from the item. ... The spell uses its normal casting time, range, and duration,"
It goes on to state that some "spells cast from" items do bypass the casting and directly give the effect. (like potions)
So there is clearly a defined (and used) mechanism that lets an item give a spell effect without casting. So it is a deliberate choice that spell scrolls, enspelled wands, and rings of spell storing do NOT invoke that mechanism. Why make the distinction if it were not important?
In fact the specific item descriptions seem to align with the description of spell casting in the new PHB. To cast a spell you meet a set of requirements (spell in head, spell slots, v/s/m components), some of these are met with items.
Then the spell is cast using it's casting time (unless specified differently) Reading a scroll puts the spell in your head, energizes the spell slot(s) and proves the material components (but not the v/s)
But the rules clearly give the DM the ability to create item(wands/spell scrolls) that act like potions/scroll of protection. Or you could house rule that some items default that way. (or you can craft it that way).