This was the real issue, imo. In LFG. That's why they have challenge runs for guild groups, and Wrath-style heroics for LFG in MoP. The Cata heroics were fine for pre-made groups that gave you some confidence people could do what was needed.. They just sucked horribly for a lot of pugs.
Looking forward to challenge runs.I don't know that raiding has become more casual, in as much as Blizzard has a more diverse player base to cater to. Pleasing one group, excludes other. It's a balancing act, that I think they're getting better at.