Additionally, 4E is actually UNBALANCED in this regard: take away a martial character's sword, his damage goes down significantly, and he gets no proficiency bonus _OR_ qualify for any special abilities like sneak attack, or fighter weapon powers. Take away an arcane/divine/primal character's implement, and they don't even care.
So I propose the following house rule, take it if you like it. Mathematically, it almost precisely works out--which is better than the current system:
Implement Keyword
Replace the last sentence in the Implement description (page 56, Player's Handbook) to the following: "Characters who do not have an implement for a power with the Implement keyword take a -2 penalty to attack rolls, and are considered weakened."
Wizards and clerics and other impliment users should still be clinging to their impliment in 4e as it is typically their only chance to hit an opponent in combat. Without that +6 impliment, they are at -6 to attacks and damage. That sucks.
Basically your houserule doesn't really add all that much, but it also doesn't really penalize impliment users who don't have theirs either. Their attacks probably won't hit anyway, and if they do it will already be for less damage.
Improvised weapons (unarmed) counts as a weapon for a fighters attacks.
But they still deal a portion less damage, and have no prof bonus, nor any feat-related bonuses. Reducing implement damage and attack rolls tries to equate to that.
Wizards and clerics and other impliment users should still be clinging to their impliment in 4e as it is typically their only chance to hit an opponent in combat. Without that +6 impliment, they are at -6 to attacks and damage. That sucks.
...fighters have the same problem with no +6 weapon?
Basically your houserule doesn't really add all that much, but it also doesn't really penalize impliment users who don't have theirs either.
Their attacks won't hit anyway--but they'll hit 10-15% more often than fighters, and they'll deal 6 less damage, but considering that's a flat 6 damage less, whereas fighters without weapons deal multipliers less _IN ADDITION TO_ 6 less (a 7d[W] rogue power with even 1 point less in weapon damage in addition to enhancement deals 13 less damage--a wizard without his equivalent staff would only deal 6 less), damage less at level 30 is a lot less than the 9-10 damage less that a fighter deals. So, again, it DOES penalize them--it puts 'unarmed magic' on the level of 'unarmed fighting'.
Of course, if you're a bow-specialized ranger, you're still hosed, huh?
Are you planning to take away all of your PCs' gear on a routine basis? That's the only reason that this would ever be an issue, and 4E is not balanced on the assumption that it'll be one.
Well, beyond the fact that responding to a TPK with "You wake up, naked, as slaves and/or food inside a goblin cave" is better for the story than "You're all dead. Who wants to play Mechwarrior?": actually, yeah, they are going to lose their gear--for the second time this campaign. First time was us waking up amnesiatic in a dungeon, but it blew because instead of a sweeping, creeping dungeon crawl, the casters just annihilated everything because at level 1, they're still at 100% strength without implements, while the fighters stood back and watched. Not a very happy omage to 3rd edition.
Now, me and my buddy swap DMing to save from DM burnout (and he's out of town this week). However, he was _JUST_ about to start a major quest line after arriving in a town via boat, but I don't want to screw that up.
Solution?
PCs get captured by pirates while traveling, stripped of gear, and have to break out of the 'pirate cove' style locale.
And before anyone says its cheesy to strip them of their gear, the circumstances of the story are... well, it fits right in with the story. They were so badly injured (repeatedly whipped by tree-trunk thick 'tentacles' of lava controlled by an elder evil) at the end of the last adventure they required hospitalization and their deva bard's healing for weeks, but the _ONLY_ boat that was going to arrive at their zombie-infested island was arriving in only a couple days.
So they were stretcher'd onto the boat when it arrived, and the deva planned to heal them from when they left port to well into their arrival at their next destination.
Except, the ship is attacked by pirates, and the heroes--being comatose--don't save the day, everyone's killed or sold into slavery. The deva _bard_ manages to convince the pirates they adventurers will be worth the time to keep alive and let him heal, so they bring them to the island, let the deva heal them inside some cages, and bam...
Party wakes up, on an island, with no gear--except this time, casters don't rock without their implements.