The difference is, the leader isn't making any assumptions that a person doesn't need to roll on a particular item because it's not appropriate for his build.
The game assigns raid loot randomly (it could be 12 pieces or it could be none) and the player decides if he will use it or not. If he will use it then he needs it and loots it. If not. He offers it for trade.
I give my friends/guildies items all the time. Even uber items like vorpals, smiters, paralysers, tomes, chaosgardes, planar girds and regular items. All of these items, I have given away at one time or another. Giving away a piece of raid loot I won't use doesn't bother me at all.
In a guild raid, the need before greed aspect can still be played out. Nothing has changed.
In a pug....... you take your chances like any other time. Just with the new system, you won't get told you can't roll on that item because it's not suitable for your build, even though the person telling you this know very little about your build or play style.