It makes sense and there is a truth to it no doubt. But have you ever been at that place were the timers were off and then the raid went to shit because people couldn't watch for the cast bars themselves? As others have said, many things have alerts and animations and the Boss does an Emote that lets you know something is starting. I believe the really skilled players pick up on all that and have the reaction speed to act on it.
I suffer from tunnel vision and baddieness. I use powerAuras to set up alerts to tell me things I shouldn't need to be told, like when my Health is below 35% because I zone out and forget to look at myself. I found the more mods I can use to play for me, the more lazy I get.