Because magic items that must be worn will fit users of
any size, a dragon can use any magic item a humanoid character
can
from Draconomicon
Essentially a dragon can wear most stuff humanoids wear.
Only armor must be made to measure.
Heh, that's why too many things are ambiguous. Kinda makes Sizing a pointless property since one can just say that the item is bigger. A character gets a graft(or naturally born) that gives no bonuses, but gives him large hands. Now that his hands are large, and magic items automatically size for the users, he now can wield a large weapon at no penalty and no feat(not counting proficiency). That seems too broken to me. I'll always hold to it needing Sizing.
Here's a scenario for you. You're medium, in your party, you also have a gnome. You defeat giants. They drop giant sized equipment(all magical). No one is strong enough to carry it. Lightbulb! The gnome touches them, they shrink because they're magic and change for his size(but no Sizing property). Wow, now they're all small, they can be carried with ease now. See how broken that is? Sorry, they need Sizing property. If I was the DM