I've seen solemn discussions of magic items in D&D and how the ancestral sword that looked so nifty at third level is outclassed by ninth level when you pick up an ordinary dagger. That the only real way around it was an evolving item that would produce new powers at higher levels.
Now, a novel about a sword, or a ring, or whatever that unfolded its powers as time went on is certainly workable. Perhaps the magic requires its wielder prove his worth, or perhaps the inexperienced user would draw too much attention with the wonders it's capable of it, so it caps them until he can take the attention.
But tossing a character a vastly overpowered item and having him wrestle with the consequence is much easier in a novel. Particularly since if he's the main character, the other characters, even if in the same party, should be less important.
And minor items can continue useful forever, partly because the character can come up with more ingenious uses for them, but partly because their power is not fixed and defined, and because the hero doesn't have to become superhuman in the course of adventure.