Regarding this statement that people keep throwing around that "You won't really lose gil because it will have the same value as it did before"

That is only true with regard to items purchased from npc's.

I highly doubt that they're going to automatically reduce the price of all market ward items by the same 10%.

That means that an item on the wards selling for 2 million gil today, will still cost 2 million gil when ARR comes out. People that might have been able to scrape up 2 million gil, will see their wallet holding only 200k. With all sources of gil (outside of the market wards) supplying less than they did before, our hapless casual gamer that no one on these forums gives a flying flea about (but which I happen to be) will find it next to impossible to scrape up the 2 million gil to buy what they want.

So, yes, we will be losing money, it's just that the people who will notice it the most, the ones that have to fight and scrimp and save and hoard it carefully, are the ones that will suffer.