I agree with you there. The money i made killing mobs and doing leves must be up to, what? 6kk the most (up until I learnt how much more money I could make with the AH). I've got 100kk at the moment, and guess what? I didn't make it buying and selling things to NPCs.

.NPCs buy things at low price
.NPC sell things at higher prices
What do you do? -> Make money at the Auction House
And guess what? Items at the AH won't have a 10% discount

This change will affect the money we have and the NPCs
The AH wont change much

And the way things are going, seems like SE wants to make making gil even more difficult (like in FFXI)

So don't fool yourselves, because dropping 10% means its going to be a lot harder to make money