Since WotLK, and especially with Cataclysm, WoW did not become more casual. Instead, it became more hardcore. I know this runs contrary to what most players believe. So, please hear me out.
Five-player content became content for those who grinded for the external reward, not content for players who played for casual fun. Grinding for epics is not casual.
The leveling game was not changed to appeal to casuals. It is too boring to be able do that. It was changed to appeal to hardcore players who wanted another twink and didn't care about how boring it is as long as it is fast. Ask any casual you know whether he likes the changes to WoW's leveling game.
Some starting zones are pretty damn hardcore. As an undead you can't win against even two mobs of your level during level 4-6. Accidental pulling of two mobs might look improbable to you, but it's certainly not improbable for a new player who still has to learn about aggro ranges and how to move his char. The leveling becomes trivial only after lvl10.
The open world, which used to be a fun game full of instant action and the chance to get a useful random drop, was turned into a dailies-only minigame, which was so repetitive that only the hardcore, who grinded for the external reward, engaged in it. Logging in daily to grind for external rewards is not casual.
The entire leveling experience is unpolished. Have a look at professions or many quests. Or low-lvl battlegrounds. Let alone the transition 60-61.
Heirlooms were very effective at catering to hardcore players. New players or casual players aren't exactly enthused that they now have to play a lot at the endgame and be part of a max-rank guild to be able to buy the heirlooms. And without heirlooms you often cannot participate in low-lvl PvP and are in many respects disadvantaged compared to hardcore players leveling a new twink. Ask a new player whether he thinks it is fair that other players run around with great looking very powerful weapons while they have to rely on drops.
Forced anonymous grouping severely diminished WoW's capability to draw new players into communities. Only the players already part of existing communities could ignore the forced anonymous grouping and group with other players they already know. Casual players, who are not part of a guild, have to group anonymously in order to progress their toon.
Raids use loot rules (badges/points) that are useful for hardcore raids to equip twinks for raiding. But most casuals never finish a raid tier in time. They can't raid at their own pace anymore since WotLK.
Guild perks give established players a serious advantage. To enjoy the same advantages, new and casual players need to join guilds they don't know. But since they don't know the players in these guilds prior to joining, they often end up in communities that don't work for them. There is no content (left) which makes players get to know other players before joining their guild.
Concluding, if Blizzard has indeed tried to make WoW more 'casual', they failed. Since the start of WotLK, the two-mio-subs-per-year growth has suddenly dropped to zero. Playing WoW today you will not find more casuals - you will find more hardcore. Make a new toon if you want to see yourself.