Again, you're mentioning the few items they have added to NPC vendors at arbitrary prices. Those items will rarely sell for more in AH than at the NPC, but there isn't any regulation on the selling price. More things sell to NPCs for far less than what you make off 1 guild leve.

The point of the index would be to help monitor the factors of supply and demand in real time, and use those figures to help regulate currency flow.

And it seems that they want to have items available through a variety of means-- meaning while some good gear is obtained through primals and etc, other types may require purchasing the items from a skilled crafter.

I still don't see any good reason why the market would not benefit from NPC participation-- it would be beneficial to both new players and seasoned players. New players would be introduced into the value of the current market with NPC prices, and older players would have additional outlets for selling goods.

NPCs shouldn't be expected to be competitive with the player market, but can help regulate those values from hyper-inflating.