Infiniti: you're making the (false, IMO) assumption that classes don't get anything for having to worry about multiple weapons/implements.
Here's the thing, though: Every class that has this split (and it just isn't an issue for classes that are pure implement builds -- not having a magic FOO on something you do really rarely (or just using your bare hands to make OAs, even) just isn't a huge deal) actually has different kinds of capabilities along the different styles of power. Bards have a melee build (uses magic weapons) and a ranged build (uses implements) -- a bard can be built using just one or the other (eg, the equivalent of a fighter who chooses to take heavy blade powers, not flail or axe powers), or you can spend a bit more or takes some feats so you can do both. Similarly, Druids are a classic example, as in beastform, they're very effective melee combattants (even without a weapon; beastform Druids make melee basics with their implement and add wisdom), but can't do ranged or area attacks; in human form they have at best a very bad basic attack without serious feat support that's frankly not worth putting into them, given that it only takes a minor action to shift to beastform. The -worst- is the Artificer -- who pays for being able to use both ranged and melee weapons -and- implements with the player having to maintain and juggle three items.
But--all classes are segmented. You're never choosing from the full list of powers unless you pay a lot to do so -- and that's intentional; remember that every class has a choice between either two primary abilities or two secondary abilities. So the fact that there's a cost for, effectively, getting access to an entire class's worth of new abilities to choose from (because nearly every class can play very effectively on just one side of their divide -- you can build an artificer that's a pure weapon build; a bard that's pure ranged or pure melee, a laser cleric or a melee cleric (and even give the laser cleric some melee attacks); a druid that spends all their time in beast form or one who only goes into it to get the minor action shift.
The only real issue here are options that are clearly better than other options. Staff is the big one (for everyone except sorcerers, who get dagger as an implement, which since it gives them a usable basic melee -and- a basic ranged attack, is a one handed, off-hand weapon, and has a higher proficiency bonus to boot, is clearly superior aside from there not being a dagger of ruin) for classes that have it as an option.
There, It's incumbent on the designers to provide cookies for the other implements that help them measure up. In general, I think implements are better than a weapon of their level (note, for example, the high crit die implements, which often also have a good power), but I'm not convinced the designers have properly balanced things (though usually the non-weapon implement at least has a pile of class-specific powers that can be better than the generic stuff. Warlocks get a ton of cool things to do with rods; songblades all have their own powers and properties as well as being weapliments for bards; totems have cool and interesting shaman and druid powers.
