Yeah, that was one of the first things that I thought of when I read how they're doing it. I just chalked it up to the fact that either the games day and encounters stuff were put together before the all of the rules were finalized or that the writers goofed. It's not like that hasn't happened in the games day stuff before. hehe.
Personally, I love how they gave +1 items to all of the games day characters even though they all have inherant bonuses of +1.
I guess, at leat concerning "bloodsand Arena" they wanted to have just one metal weapon in the group to make the players and the DM see what difference it makes and that it's "iconic" and "cool". It was even won as first prize in a arena tournament, so it shows that it is rare indeed.
I will give my players some magic items, too. Probably as much as the treasure parcels tell (plus adding some money-worth favors) even with the inherant enhancement bonuses. I want to give the players the possibility to decide which item has the funnies or worthiest powers and properties, not only the highest enhancement. Brings in another choice for them and it's not that much up the "I wanna have the highest value" anymore. And they can carry around multiple (magic) weapons when one breaks (and if they get more treasure than WotC planned they have some "spare money" to repair broken weapons).
Did they ever explain why there is no metal?
In the 4e DS book they don't tell you that as far as I remember. But you will find only one named iron mine or iron mines compound which is next to and under the control of Tyr.