It's debatable whether the author of that series does a good job in having so many different central characters.
Oh, absolutely! I really didn't care for the way the oodles and oodles of viewpoint characters were handled in GoT, personally, but what I was objecting to was the notion that somehow there can be only one protagonist BY DEFINITION. I think that series is a fairly well-known one that's a good counterexample to that argument, that's all. Whether or not it's a
good idea to have more than one protagonist is a different question entirely!
For my part, I tend to get leery over having multiple central characters, which almost inevitably means multiple POV's. You really compound problems of pacing and structure when you have two or more mostly-independent storylines going on, so in my opinion you
really have to have something big to gain by using multiple protagonists before you should take on that kind of logistic writing nightmare.
I recently read
a great essay on POV that comes to similar conclusions. Basically, the premise is that limiting your viewpoint is valuable because it helps you know what you
shouldn't show in the story. When you have tons of viewpoint characters or a near-omniscient POV, the temptation is to show
everything, but the essence of writing is really about choosing what's truly important and cutting out all the rest. Sticking to one or only a couple main characters helps you write a more focused story just by the nature of the setup. (There are lots of rly rly great essays on that site, for what it's worth, plus loads of practical info on the script-writing business, so definitely something to check out if that's the way you plan on going with your writing.)