Its Blizzard's way of mareketing and making money.
Now, more descriptively.
Personally, I don't really care if carrier is going to be removed or not.
But, I know it will be back by the third expansion, "Legacy of the Void"
First reason is that, Carrier is the symbol and captial ship of Protoss since the first Starcraft.
Just because players rarely choose to make fleet beacon to make the carriers, doesn't mean Blizzard should just take one unit out of the game completely and replace it with another unit.
In more correct sense, it's more realistic and idealistic to keep the carrier, and add a new unit. (Since fleet beacon tech/producing carrier isn't often)
Basically, Blizzard likes to play with our heads and minds. "playing with you" / almost toying with people. It's almost disgusting if you think about it in a bigger scope.
Blizzard never officially let the players know about expected release dates of their next installment such as Diablo 3 and HoTS expansion. They like to make people anxious, desperate, and be-ready of state of mind to buy the game when it is released.
It's ugly marketing to make ugly sum of money. Blizzard should be more straight-forward with people and their customers.
The carrier will return in the third expansion, because not only I think carrier is crucial and symbolic protoss unit, but without it I feel its like leaving an empty hole in protoss basis, 'intentionally".
It's Blizzard's way to do things, they cover it up by saying it's for the better game-play and balance, but fully "on top of that", its important to realize that its their ugly way of marketing, and making money off of "You"
Realize it. WoW, and Starcraft 2 for example, anyone with decent computer can run the game pretty nicely. Look at WoW for ex. its 3d/2d graphic engine which allows/allowed many many people through-out the world to run it nicely when it was released. Starcraft 2/ Diablo 3 is the same case. It doesn't require high-end graphic cards to run it. Why? to sell more .Why? to sell more "and more". What I'm saying is, Blizzard may be the top game selling company, but I feel they don't "deserve" the title as the best game-making company. Clearly seems to me that Blizzard is pretty insane to make money than caring much about making a perfect game that everyone wants and waits. I feel they don't deserve to have this much attention anymore, when they do have the potential to make truly the awsome games.
Its shame. But anyways, I'm pretty sure Carrier will be back by the third expansion.