Still waiting for some evidence that he actually derived the concept from there, instead of coming up with it on his own, or from some other source. When you think about it (and I read somewhere else pointing this out), it's pretty much the mirror image of his previous series, Island in the Sea of Time: one has a world suddenly gaining a technological leg up thanks the big magical event, the other has a world suddenly regressing in technology thanks to the big magical event. It's easy to imagine him thinking, "I want to do something about what happened to the Earth Nantucket left behind... hmmm, maybe they're dealing with kind of the opposite situation, and they're actually regressing in technology," and then, once the idea was formed by him, maybe reflecting back on an old story he once enjoyed that also used that premise, and drew some inspiration, while also introducing plenty of elements of his own and a completely different storyline. Hard to say.
Not idiosyncratic at all, as I said, if you're writing a story where technology fails and people are forced to rely on medieval weaponry, the people who, for a hobby, practice extensively with such weaponry are naturally going to have a leg up on everybody else. If I were writing a story with that premise, it'd be a part of mine, too. Just like it'd be that staying in a huge city immediately after the change would be a deathtrap (apparently, Ariel dispenses with this, by just having most of the population disappear. Fairly significant difference in plots... in addition to the fact that, from what I can tell, Ariel starts many years after their Change, and the Dies the Fire universe follows the characters directly through it, and all the growing pains and learning what works and doesn't).
Also following fairly logically. You've got a defended fortress. You want to get past their defenses without confronting them directly. You've got modern inventions, but no modern technology. Slipping in with a hang glider is about your only option aside from a balloon, and balloons are easier to spot and shoot down. And remember, Stirling's story doesn't have this additional element of magical creatures that it can ALSO draw on for other options, Boyett's does. He could have written the attack on the fortress being facilitated by a pegasus. Stirling didn't have that option.
Can't speak to the similarities in the characters. Being generous (and, again, it's not that much of a stretch to a character who is into fantasy in a book where the world is thrust back to medieval tech), and, in my not having read Ariel, I'll allow for the possibility that maybe they're pretty much identical in personality and circumstances, including the extensive family ties to many of the other main characters, rather than that they share one particularly notable trait. So, okay, maybe you've got ONE point. There are going to be plenty of similarities in any two books, particularly any that share a basic premise. Any others?
Another example of 'fairly obvious stuff' is a superior bow (or for that matter, anything) made before the change out of high tech materials, that is now much more valuable because although it still works, it can't be made any more. Does Ariel have that? I don't know. But if it did, I wouldn't be at all surprised. How about a character dying of what is, in the normal world, a fairly easily treatable disease?
How about anything you can point to that's nearly identical that's NOT related to the premise?
And you think that when he shamelessly stole a book's plot without credit, he would attempt to hide it by also using the same subtitle? Ooookay.
None? You don't think he was influenced by any other books but the one you insist he stole from? If so, he's incredibly inventive, because, reading a plot synopsis of Ariel, it doesn't sound anything like Dies the Fire at ALL. For one thing, the Ariel, in Ariel, refers to a freaking UNICORN the main character encounters and befriends and the plot revolves around. I mean, that's a pretty substantive change. Stirling's book is mostly how different groups of people survive a changed world build a new society and the politics and conflicts that follow, rather than one man's coming-of-age adventure with a unicorn through a world that's already changed many years ago. There's not even a side character that can't return home until he kills a dragon, or anything else, in Stirling's work as far as I read. If Stirling had no other influences, than he's some idiot-savant font of creativity.
I didn't know before this conversation, but look what I found in just a few searches:
" (To be fair, Stirling acknowledges the debt, as he offers the new edition its most prominent blurb.)"
and from http://librarydad.blogspot.ca/2010/02/steven-r-boyett-vs-s-m-stirling.html (in the comments, it's anonymous so it could be bull, but it claims to be Stirling):
"Steve Boyett's work was one of my inspirations and I'm a great fan of his; that's why I did a blurb for "Elegy Beach"."
So, yep, he has given it some kind of acknowledgement, a fairly significant one.
So we're left with a basic premise that inspired a completely different work that shares a few elements in common. I see no problem here. This is how art happens.
The situations are not at all analogous, considering the paintings in that example are virtually exactly the same in every way. These books are not. See the absence of a unicorn for Exhibit A. A comparable example would be a person like you complaining that that any picture of a spaceship towing an asteroid with some kind of structure on it stole from Chris Foss, even if the spaceship, asteroid, and structure looked nothing alike (except in that spaceships tend to have certain features in common with other spaceships, asteroids with asteroids, and structures with structures), and there was also an alien space battle and black hole. And no, I'd have no problem with that situation (the similarity in concepts that is, I'd think the complainer's a bit off-kilter). Especially if the artist's also said, "Yeah, I really liked that Chris Foss painting and I wanted to do something with an inhabited asteroid being towed."