On retail, with each new raid tier that was released Blizzard made it so Heroic 5 mans dungeons rewarded badges that could be used to buy gear as good as the previous tier of raid gear, thus making it redundant to run those raids anymore.
Did that happen here, or did the devs make it so if you wanted to raid the harder stuff, you had to progress through the raids? Naxx -> Ulduar -> ToC etc
