I think your last paragraph hits it spot on, it's about what people find fun.

On the opposite side of micro transactions, we constantly hear advertisements from banks or other businesses that rally against micro transactions. "Stop paying for hidden fees" is the major one I can recall at the moment. I feel that this is a stigma microtransactions are going to have to overcome before becoming completely acceptable.

Yes, people pay for iPhone apps, or small things like that. But as you know, nobody pays more money for ketchup at McDonalds. Sure, chick-fil-a has managed to charge people extra money for their sauces, 25 cents a sauce packet, but there's a breaking point where you just don't pay anymore. You don't buy a burger one slice of bread or piece of pickle at a time. And that, in my opinion, is the problem with some of the companies that are attempting to use micro transaction. You don't charge piece meal for the product, where it's unfinished without, but you can charge for frivolities.

It's about the game world as well. When some people playing your MMO can just buy the end game whatever with outside money, then it trivializes all of the rewards players are supposed to be working towards. Take gold selling companies for example. Gamers hate them for more reasons then just the spam, as do game companies, because they trivialize parts of the game itself. If you can just buy the end product with real life cash, then what's the point of the game. Micro transactions in games are a different beast then they are IRL. Macro transactions such as server transfers are different then spending money on something within the game world such as a more powerful weapon than anyone else has access to.