Accuracy Implements are just the answer to Superior Weapons.
No, they are not. Same type Superior Weapons do not give a bonus to hit, just a bonus to damage. Accuracy Implements give a bonus to hit. Bonuses to hit are more rare and valuable than bonuses to damage. Apples and oranges.
The original monster manual was set up where AC tended to be (on average over the entire population of monsters) ~1.4 points higher than Fort, ~2.8 higher than Reflex and ~3.3 points higher than Will. Give or take.
So, most bladed weapons were pretty much the equivalent to a normal implement vs. either Reflex or Will and non-bladed weapons tended to be slightly inferior (at least with regard to "to hit").
Implements were not as good vs. Fort as weapons are vs. AC, but it doesn't make sense to make Reflex and Will attacks even better because Fort attacks are worse. It would have been ok to make Accuracy Implements that only worked with Fort powers, but that's not what they did.
With the introduction of MM2 and later monsters, WotC started switching defenses up a lot. Fort tends to not be as high as in MM1, Reflex tends to be higher, and Will tends to be about the same.
But, this doesn't take into account a major advantage that implement users have over weapon users.
If the player of a PC with an implement notices or intuits that one defense is weaker than the others for a given foe, he can have his PC use powers that target that defense. He has 3 different defenses where he can try to target the weakest one. Weapon users almost always attack AC, so they tend to be at a disadvantage here.
So although monster defenses tend to be ~2.5 lower than AC which would give a very slight edge (pun intended) to bladed weapon PCs (and a slight disadvantage to non-bladed weapons), the fact that the implement PC can switch to a weaker defense easily negates this slight advantage.
Adding +1 to hit on top of that advantage is a bit unbalanced. There are a ton of ways to add extra damage, but adding a continuous plus to hit shouldn't be in the game and is power creep.