Price is key. I can't see how anyone would be upset about paying 99 cents for an extra costume or whatever, that would not have appeared in the game otherwise.
Often a developer wont have time to add everything to the game that they want to before release. I'm not talking about bugs that don't get fixed (even though that happens too) but legitimate content like levels, costumes, etc. It's not about intentionally leaving stuff out to rip off gamers, it's about simply not having enough time. And usually this extra content will never be seen. If it is, it's seen in a rerelease of the game (like is done with movies/albums)
I don't see the issue for giving devs incentive to add these little extras if they want for a price. Some devs may not (just like PC devs add more multiplayer maps for free, or Itagaki gave away the hurrricane packs for free), but if some devs do...who cares? Don't buy it. I work for game studio now, and I know we would have spent time on extra shit if there was a worthwhile way of distributing it. But since there was not, and we didn't have time to finish what we had before release..no one will see it
That said, this Kameo thing sounds stupid
. An Xmas gift that you pay for. Woo. And the fact that Rare is first party doesn't help. It is a true test to see if they can make money off this sort of thing though. M$ finding worth with a truly worthless addition. My guess: people will buy it if it's 99 cents. People buy even more worthless shit for more like ringtones, cellphone wallpaper, etc.