The audio plugin example is typical because the vast majority of music production software exhibits a great deal of skeuomorphism. I personally don't like this because it increases the cognitive load in trying to figure out an interface, and I don't feel like it helps make things more intuitive than a non-skeuomorphic interface -- rather the opposite, it becomes more confusing.
This is one of the reasons I like Ableton Live ( http://www.ableton.com/suite-8 ): it has a simple, consistent user interface elements and the entire user interface happens to be vector based. Not only is it easy to navigate and understand, but the fact that it is vector based allows it to have a resolution-independent interface that can be zoomed in/out. Which addresses another problem with music production software: they tend to use tiny fonts and other UI elements which makes it hard to read when used with a high-PPI monitor and/or when the monitor is far enough away from the user (which seems to often be case in many studio setups). And once you've done a highly graphical skeuomorphic interface that uses lots of bitmaps, scaling doesn't always happen smoothly.
On the other hand, many people like skeuomorphic interfaces when they've had past experience with actual audio hardware. Reason ( http://www.propellerheads.se/products/reason/ ) is one such example where the interface is so skeuomorphic that is often considered a hardware simulator. People who have past experience with such hardware often love Reason because they are able to draw upon past experience to understand the interface. I suppose in this case, this is a very appropriate use of skeuomorphism.
People like me who don't have experience with such hardware aren't necessarily going to appreciate this, though some people will enjoy it even without past experience with hardware because some people simply enjoy visually appealing graphical interfaces. So it's a tough call which group of people is in the majority and who you want to cater to. Personally I like music/audio software to focus on it's core task of being a music creation tool, and less on being graphically impressive; but that's just me.
The other thing to consider is that audio processing is resource intensive. Many times you need to run many things at once and performance suffers.
Guess what else is resource intensive? Graphics. So everytime you have gratuitous graphics (e.g. a guitar plug-in that has one or two controls but goes to ridiculous lengths to reproduce a graphical image of, say, a guitar pedal), it takes away some of your resources.
I think you're right though. The interface is aimed at people who are used to looking at gear. That is the intended audience. They wanted to sell to the same people who were buying physical gear. Unfortunately it alienates anyone who understands how to actually use a computer beyond pointing and clicking or keyboard shortcuts.
I mentioned it in another comment in this thread, but if you want to see how things could be done in a "UNIX way", check out snd from the guys at Stanford CCRMA. It has a long history, longer than Ableton, probably as old as Sound Designer, the precursor to Pro Tools, though I'd have to check the dates. These guys clearly "get it". This is how computers and audio should intersect.
But, functionally, it's not a substitute for MOTU, Ableton or Digidesign, unfortunately.
I really shouldn't have said "UNIX way". It really is more a "LISP way" I guess. LISP predates UNIX. My point was just that it's an "interface" that's more in line with how computers actually work.
This is one of the reasons I like Ableton Live ( http://www.ableton.com/suite-8 ): it has a simple, consistent user interface elements and the entire user interface happens to be vector based. Not only is it easy to navigate and understand, but the fact that it is vector based allows it to have a resolution-independent interface that can be zoomed in/out. Which addresses another problem with music production software: they tend to use tiny fonts and other UI elements which makes it hard to read when used with a high-PPI monitor and/or when the monitor is far enough away from the user (which seems to often be case in many studio setups). And once you've done a highly graphical skeuomorphic interface that uses lots of bitmaps, scaling doesn't always happen smoothly.
On the other hand, many people like skeuomorphic interfaces when they've had past experience with actual audio hardware. Reason ( http://www.propellerheads.se/products/reason/ ) is one such example where the interface is so skeuomorphic that is often considered a hardware simulator. People who have past experience with such hardware often love Reason because they are able to draw upon past experience to understand the interface. I suppose in this case, this is a very appropriate use of skeuomorphism.
People like me who don't have experience with such hardware aren't necessarily going to appreciate this, though some people will enjoy it even without past experience with hardware because some people simply enjoy visually appealing graphical interfaces. So it's a tough call which group of people is in the majority and who you want to cater to. Personally I like music/audio software to focus on it's core task of being a music creation tool, and less on being graphically impressive; but that's just me.