The Free-To-Play Triangle [Game Economics] - What Games Are
Ottway Ducard stashed this in games
"The triangle intentionally ignores aesthetic items with no gameplay value, such as decorations or status items. While purely aesthetic objects can be a delightful part of any game experience (from wallpaper choices in Restaurant City to hats in Team Fortress), they do not affect the fun of the game. The fun is what the triangle seeks to protect, and as long as it is protected I see no reason why you can't sell as many decorations as you want.
Sometimes players like to give each other virtual Christmas trees in-game. Why not let them?"