^^^Again, where are you guys getting these stats from? I've known it to be a leading tool in recording and mixing...but this is the 1st I've heard of Mastering especially for "majors".
I could still be living in the dark ages, but most M.E.'s I know of still rely heavily on hardware and contained mastering programs(
Wavelab/
Soundforge). Other than that, I know of a few industry elites who use
Sequoia. I'm not saying Pro Tools can't master, I'm saying I've never seen a Mastering engineer run out to get Pro Tools because it was the "professional choice" for mastering.
It's mastering, you don't have to reopen files like you do when recording/mixing(compatibility plays a huge role in why people use Pro Tools), most M.E.'s I know each have their own individual setup. You don't see the same thing in many mastering environments because everyone relies on their own individual set of tools. A mastering setup is where you usually find speakers/monitors you've never heard of(or not very popular), the randomest processors fused into a chain, weird and unorthodox methods of things being done.
It's not a contained enough process to say "Pro Tools is needed" or even used heavily. I've seen M.E.'s who use it(myself for 1, simply because I own it for recording, no other reason), but seen just as many use stuff that I've never heard of many people using for recording like Adobe Audition. I know a few M.E.'s who think that's the holy grail of mastering. They also tend to rely on more hulked up PCs than Macs while in other stages of music I see more Macs than PCs. All just from my experience, so others may see things differently.
Asking about gear for mastering is like asking about the best/most used guitar amp or best/most used tool for making beats. There are certain areas of music where everyone kinda does their own thing.
The only thing I've ever known Pro Tools to be known for is the recording/mixing process simply because if everyone used it, transferring files was done more easily.
EDIT: Nvmd, I did a quick google search, Pro Tools and Waves plugs seem to be the choice of DIYer's. Irony is, that kind of makes Pro Tools and Waves the FL Studio of the Mastering world...does it not?