I wouldn't say it killed raiding... it did kill 25man raid guilds though. The few that are out there, are the exception that confirms this rule. There are servers, without ONE 25man raiding guild.
For the first time, since its foundation 6 years ago, my guild took a break from raiding, cuz we cant find any recruits willing to raid 25man. While we wait for MoP to land, we stopped raiding.
However, i dont think this is related to "casualization", as people call it.