Well, I tend to look at it like this:
If you look at the history of DAW's in general, Pro Tools was the first real multitrack system that was affordable, and understandable. It wasn't designed for midi work, just audio, and had hardware DSP available at a time when computers didn't have the power that they do today.
It became like a Studer (I imagine only a few people will know what I'm talking about, so the rest use google and find out some of the history of the recording arts ;-) every "pro" studio that got into digital audio used Protools. There were other system, and some, like the RADAR, were based on hard drives and great A?D conversion, better than Digidesigns, BUT digi was already so far ahead once TDM became the norm, that it was very hard for other types of DAW's to really catch on.
Midi apps evolved into DAWS: Logic came from the Atari days, and in the beginning there was Performer on the Mac, Notator (one day to be Logic ) on the Atari, as well as SMPTE Tracks Pro, an awesome Midi sequencer that died off. Opcode, who had Vision, became the first 3d party app to add on direct to disc recording, and became the first audio/midi daw... Opcode also was the leader when it came to developing the midi spec we take for granted today, and standard midi files.
Over time, the whole scene evolved into today, where every DAW does midi, and direct to disc recording. Protools is the main Hardware and DSP based DAW, and in north america Logic is the big sequencer/daw with Cubase being the leader in Europe.
The all pretty much do audio and midi, have built in virtual instruments and effects. Cubase was the company that developed the VST standard that AU came out of, but for the record, Propellerheads was the creator of the first VI: Rebirth.
I imagine in time that they will all become more or less the same app (as they seem to be heading that way today), and the look and feel with be the thing that will appeal to the end user.
My bottom line: when I started out 27 years ago, it was 24 track tape, big consoles, and a few effects (reverb by spring, or a real room), some digital effects were on the scene, but what that evolved into is so much more than I ever imagined at the time. And I have to admit being very happy to have watched it unfold... I (as do the old timers around here) have a unique understanding of recording, and often we have a strong appreciation for the tools we have today. To me it's like a scifi show episode, but I actually live it every day.
Sadly, the "art" or recording, and writing, in my opinion, is suffering. Most new "engineers" don't have a clue how a compressor actually works, or the theory of eq, ways to actually mic up something... I have done sessions at Capitol here in LA with a real orchestra, a great engineer, and a producer who has been doing it since I was a baby... one or 2 takes, and you're done, and it sounds like heaven. That session was magic, as was the one with the band from Chile who couldn't speak english, or the one watching one of my heros writing a hit song in a room with a band... I am saddened that this part of what we do is being lost to technology and the way we, as artists, have to ( or choose to) use our tools because of the economic situation today...
Anyways, I guess the point is, Protools was the first big DAW, and they not only named it well "Pro Tools" but were able to deliver a system that was close enough to the familiar was guys recorded, and was faster, and allowed them to do things that could be done with tape, but much much faster.
So, I hope you liked my little history lesson. I hope it inspires one or 2 of you to check out some of the books out there by a few of the guys who have been doing this kind of thing from the beginning (Recording the Beatles is a mother load of information
http://www.recordingthebeatles.com/ ) and if you can get into a big studio and be a fly on the wall, please do. It might be one of the most inspiring moments of your life, and it also might be one of the last times that you will be able to if things continue to head the way they are going...