It would suck if it was the same set or similar looking sets. However, most people I know vendor their challenge mode sets for the 200g. Almost everyone I know did it for the achievements, the mount, and/or the teleport spell. I know of no one that did it to transmog.
Actually, let me rephrase that, I know of nobody who would do it for the transmog that is able to do it without being carried. The fashionista crowd and the min/max crowd don't really overlap.
As for selling virtual fashion for real currency, I really couldn't be bothered to care. If people want to pay money to gain a non-advantage in a virtual world, so be it.
Regarding monetization models, what's the big deal? The purpose of the store-bought stuff is to give customers multiple price points. The purpose of multiple price points is to capture consumer surplus. All companies either do it or want to do it. The only difference here is that Blizzard is not offering a price point below $12 a month.
It almost seem like that most of the people complaining don't actually have a wow sub and are just not happy that their favorite failing MMO couldn't do it. This is kind of funny, as you dont usually hear this in other industries. You don't see VISA customers complaining about AmEx's annual fees on top of the larger % cut they take on purchases. You don't see McDonald customers calling people who dine at steakhouses 'chumps'.