looking at it from a social dynamic perspective, I think there is little difference between raiding and grouping, but more social benefits in raiding than grouping.
In a group, as in a raid you need others to help succeed. The only differennce in a raid is you need more. The social benefit is you are not limited to your standard group if you need a group in the future because you have all those you have raided with- and by extention "trust" (trial by fire sort of thing) - to choose from to fill future groups.
The loot dynamic of raids is similar to questing in that, one person needs help to do/get something and others come to help that one person. The unwritten social contract is, this one person helped will be available 5 times to help each of those that helped on the one quest. Like in a raid, there are few uber loots, so all raiders are motivated to engage in the same content to get a chance at uber loots. All come to help the one, or the few because one day, it could be me. (the needs of the many far outweigh the needs fo the few or the one, but sometimes, the needs of the one outweigh the needs of the many...Spock!)
Raiding is sort of an extention of grouping; motivated by loots but depending on more succesfull and sophisticated social interaction.
The developmental challenge is to create an encounter that does not realy too heavily on social interaction but depends on social interaction. Case in point: WOW dungeon Finder and dungeon design, relies on NO social interaction. "Other" encounter designs rely on people communicating with each other- in typing time or in voice time. Personally, I like the typos that come with frantic communication that are understood! "OM NBPPS!"(ON BOSS!) lol.