I'm surprised! A little less so in that I've noticed PT mentioned very little on this forum.... but it seems like most of the studios I see in magazines or engineers I hear interviewed (few, mind you....I'm far from an expert researcher in the matter) mention PT at some point. How did it get so popular if it's not that tight?
PT became standard more because of a "in the right place at the right time" factor than anything else. As boz has said, they were really the first ones to do it right. Earliest in the days of digital multitrack editing they were virtually (though not quite literally) the only game in town.. So when the bleeding edge studios wanted their new toys, PT was the way to go.
Then the idea of "standardization" took over. See, unlike many 21st century home recorders, pro tracking engineers, mixing engineers and producers in the Big Boy studios of the 20th century might work on album A in studio X, but album B in studio Y, and so forth. While they may have had "home court" studios they preferred, they had to move from studio to studio from project to project depending upon the budget, the preferences of the producer or label, available of schedule time, etc. It's often still like this today in the pro ranks, though maybe not quite as rampant as it used to be.
With this in mind, studios wanted to have gear and software that the engineers "knew" and/or wanted. An engineer doesn't want to learn how to use something new whenever they walk into a new studio. So PT became the standard for standard's sake; every pro learned PT, and then could use it wherever they went (with a few exceptions, of course). This is a similar story to the "standard" nearfield monitor called the Yamaha NS-10. Every studio wanted them so that the engineer had a familiar-sounding base to work with.
Now in the home studio, PT is not quite the standard for a few reasons. The first of which is that, contrary to popular myth, Pro Tools is not "software" per se, it's an integrated system of hardware and software. That is, you cannot just go out an buy just any hardware A/D interface you want and buy a copy of PT software to run with it. You have to buy the specific hardware and the software comes with it, and there are only a small handful of brands of hardware with which you can do that.
Second is that the full-blow PT hardware/software system as used in the Big Boy studios is not cheap stuff, much of it beyond the budget of your average home wrecker. Now, to counter that, the makers of PT have released economy versions of both the hardware and software that is affordable. But the affordable stuff isn't really any better than many of the third party brands out there, and in some cases some of the cheap hardware is a lot worse.
Third, many home recorders - especially the self-recording amateurs - don't necessarily care about standardization or compatibility with other studios or with the ability to use other studios, so for them they want the most bang for the buck, which for them may be some 3rd party stuff and not necessarily PT.
So, yes, PT is still very much a "standard" in pro studios - though certainly not ubiquitous - but is far from standard in home studios.
G.