I'm not sure "most" is accurate - and certainly not for divine implements.
From my search of the compendium -
Pact weapons and songblades/bows generally work that way (act as a "warlock/bard implement"), as well as the various shaman ones (totemic ones + alsphair spear) which acts as a shaman implements.
As well, Spellblades gain stuff when "used as an arcane implement" meaning that they gain whatever advantage based on their specific weapliment type.
As for divine weapon, from my review they almost all act as holy symbols (rather than just implements - see Bradaman's weapon, Crusader's weapon, Lion's hear hammer, Unforgettable cudgel, Weapon of Evil Undone, Scepter of Bane, Disrupting Weapon, Holy Avenger & the various diety specific weapons)
The only exceptions are Weapon of Oaths fulfilled, and Vigilant Blade.
So I agree with your point if you are a bard, shaman or warlock - but not for divine characters.