I think the message here is pretty clear, they feel like you should focus on one character and one spec in particular.
Its a fair stance, if you've been playing the same spec from the start of the expansion you should have all the legendaries for your spec and if you played enough you might even have all the legendaries for your class, which is what they are addressing now with the legendary boxes for alts.
I don't like it, personally, because I tend to get bored and swapping characters every tier helps me stay interested, but I know a lot of people who just stick to playing the one spec.
Feels odd to have such an hard stance on a game that is generally so casual friendly but I guess they figure if you are casual you shouldn't really care about the best legendaries and getting any two is already quick enough.