That "time where 100% of in-game items would be obtainable" you're remembering so fondly was also a time of "you got what the budget allowed them to create and not a drop more". Times change, as do business models. It's not about "needing" money to support the game. It's about expanding your business as a whole, not just one specific IP. Could SE run FFXIV on subs alone? Probably. Would that limit how much they could invest in expansions and content patches? DEFINITELY.
Your opinion that someone is a "sucker" for paying for something they want is noted, but it's just that, an opinion. I certainly don't feel like a sucker for buying the Thancred Modish outfit. I've used pieces of it for various outfits and its brought me a great deal of pleasure being able to make my character look the way I want him to. I'd wager others who have made purchases don't feel like suckers either. Just remember that those extra dollars people spend on the store are benfitting you directly by increasing the available budget for future FFXIV content. From my perspective, I'd say "thank you" to those people for helping the game I play grow. But that's just me.
The point that you may be missing however is that there is a market for these things, else SE wouldn't bother making them. Are they "taking advantage"? Mmmm, I suppose that's not inaccurate. They are "taking advantage" of a tap-able revenue source to expand the available resources to develop FFXIV and other SE intellectual properties. At the same time they are providing additional things for FFXIV players that go beyond the allotted budget, and apparently meeting a demand of their player base by doing so.
For me personally, there's very little I find desirable from the Mogstation, but damn if my eyes didn't light up at the prospect of getting that Thancred Modish outfit... something I would NEVER have gotten to have if they hadn't went above and beyond the allotted budget to make it useable by players, and put it into the store.