This isn't true, but it takes proper design to implement effectively. All people want is gear that makes them relatively stronger in the world. They don't necessarily want rewards from larger group content. The most obvious solution is to adjust the scaling so that the open world is much more available regardless of your gear, so that the upgrades you do receive are noticeably stronger.
The less obvious and more technically challenging solution is to segregate gear effectivenes based on the content it comes from. I've detailed this in WoW threads, but essentially PvP, World, and Raid gear. They all share power budgets, with the exception that they have an additional rating based on the content. PvP Power/Defense, World Power/Defense, Raid Power/Defense.
It makes it so that any gear from any content is feasible as entrance into the other, but you will never be remotely close to the power that someone focusing in that content can be. The problem is that this has a few caveats, most of which would just be raiders complaining that they aren't super leetsauce at farming/dailies, but nothing is stopping them from getting the World gear either.
So in summary, people don't want raid gear...they just want the power against the world.