Exactly.  Which is one route to product improvement, if you want to improve it.  I think the "UNIX" philosophy will prevent any software created to become a leader and success.  Providing things users want, whether developers want it or not, is what it takes to be successful.  Otherwise, it's just a hobby.  The philosophy may be the biggest impediment to being seriously considered by the majority of computer users, and why the software created under the philosophy will never seriously put a dent in commercial software.

The Unix philosophy is for each application to do one thing, but do it well. It's the "do it well" part that's important. Yes, Inkscape could support JPEG or a myriad other formats. But each format has options, settings, metadata and more. I'd rather have one conversion application that handles all the options on all the formats well, rather than have every application on my system reimplementing the code time and time again, each with a slightly different UI and list of supported features.

You would prefer the latter, it seems. That's fine, you're welcome to use monolithic software that works in that way. If you want Inkscape to work like that, you're also welcome to contribute code to make it do so. The devs don't have to accept it, but then you're also welcome to fork the code and create your own monolithic application. Or pay someone else to do it, if you're not a developer.

No, I don't really expect you to do any of that, but you could in principle. You can do it because Inkscape is Free Software, and as such it's developed by a group of people who *have* contributed code, time, or money to make it do what they want. For many of them it *is* "just a hobby", and that's not a bad thing.

I do find it interesting that you spend half your time worrying about people with old computers that don't have much disk space, memory or processing power, and the other half wanting monolithic applications that duplicate each others' functionality.

Standards will always be a moving target.  There's no way around that.  But from what I see, JPG is currently the most popular bitmapped format.  Not PNG.  Granted, PNG has some advantages, but are the advantages needed by most users?  I'd bet not.  Just like a Kenworth has advantages over a Ford F-150, not everyone needs a Kenworth.  <G>

Perhaps you should check out the Inkscape forum and see how often people complain that their images are being exported with a white background (because they've used "Save As Cairo PNG" rather than "Export Bitmap"). No, not everyone needs transparency, but I think it's a more popular request than you might realise. Transparency is often needed in DTP applications, but even more so for web pages, icons in applications, sprites in games and so on - all of which are frequently created using Inkscape.

There's been transparency of one sort or another for a mighty long time. Before PNG, and before GIF's one-bit transparency, even. Heck, if you want to go back far enough we were engraving images into plates of metal, coating them in ink, and pressing them onto the page. And you know what... they included transparency! Any part where the ink didn't appear was implicitly transparent.
But, how much was transparency supported in computer software?

It's been well supported by professional DTP software for many, many years, if only in the form of applying clipping paths to images. Alpha channels are a more recent addition, but I imagine that professional DTP applications have been supporting them for at least 15 years, if not longer. I'm no software historian though, so I'm happy to be proved wrong on that front.

But does it really matter whether or not it was supported 20 years ago? Any DTP application worth mentioning that's been released in the past decade supports it, which is why I suggested that an application without it is "broken".

To me, broken is something that doesn't work, not something that's missing.

Tomayto, tomahto. As far as I'm concerned "missing" standard bits of functionality results in something that "doesn't work". Perhaps it's not "broken" by one particular dictionary definition, but it is in the colloquial sense that the term is used with respect to software. Feel free to mentally replace "broken" with "is missing some functionality that I consider to be vital" in all my emails though ;)