I don't see why people don't go for Need/Greed. If you're a guild, you just trust your members downright. If someone ninjas, kick them out. You're in a raiding guild, they'll want to stay if you're progressing through content, they won't risk having no loot, or raids, for than one shiny helm. I've always ran a Need / Greed MS / OS loot and never been ninja'd by a guildy.