Would that have anything to do with the relative shortness of the neck versus that of a guitar?
I’ve seen it claimed that it “makes sense for an instrument tuned in fifths,” but I can’t think what earthly difference that makes. I think the use of the 9 on most guitars vs. the 10 on most mandos has more to do with “We’ve always done it this way.”
Speaking of the shortness of the neck, though, check out this vintage instrument. Now at a glance, wouldn’t you expect that double dot where the neck joins the body to mark the octave?
The markers are very helpful. I depend on them to orient myself on the fretboard. It’s important that nearly all guitars have them in the same locations. It would be frustrating to play a non standard one.
I had wondered if there was some music theory behind their placement. But it doesn’t have to be. Sometimes standardized markers just evolve because they are efficient. Like the placement of numbers on a clock. 12 didn’t have to be exactly top center on the dial circle.
Interesting. Yeah, you’d think that double dot and that single dot at the 12th fret would change places. What’s a mandolin have, 18 frets?
Also, don’t the fret markers help out to more quickly figure out tablature than if they weren’t there? I know they help me.
I think as long as there are edge dot markers for the player to see, the markers on the fingerboard itself are unneeded. UNLESS you’re in the habit of playing, now and then, with another guitarist. I think it’s nice to be able to see what he’s playing (and for him to see what you’re playing) and fingerboard markers make that easier to see.
And yes, it’s possible to go overboard with fingerboard inlay work. Still, nowadays, I wish when I ordered my Martin from the Custom Shop (via Mandolin Brothers) I had thought to order “diamond and square” or “42 style snowflake” markers.
It varies. I’ve seen 'em go as high as 29 frets (two octaves and a fourth). Commonly the ones with very high frets have fretboards that extend out under the highest strings only–note that the one in the picture I linked to has such an extension for the 19th and 20th frets.
Yeah, that’s the only time when I can see the fretboard markers being anything but decoration, when one of us is lost. The edge markers are indispensable for me, though. I know someone who put tiny brass nails in the edge of a Kay’s fretboard that lacked them, ages before it became collectible.
Even then, I do lust after a SG with some split block inlays, maybe a bound fretboard. It doesn’t matter that I wont see it once it’s strapped in front of my belly. I do think that anything far beyond the standard positions being inlaid becomes gaudy, but what’s wrong with having pretty tools, WordMan?
Wow. Ok, I looked at the “Dragon” PRS. My lord, I smoke a lot of pot, but they have to be burning bales of it in the HVAC system to think that’s an improvement. That’s just mucking up what’s generally a pretty shape, maybe the prettiest shape to be introduced in my lifetime.
To be clear, there is nothing wrong with having pretty tools. Well, except for the phrase “pretty tools.” 
Anyone should get whatever guitar they like and which keeps them playing. To me - and only to me - I tend to favor plain guitars whose beauty/attractiveness is more, I dunno, “form follows function.” I have a couple of Tele’s, a Martin D-18, a Gibson J-45, etc. - all models with minimal bling. I started to see this in my preferences and kinda went with it. I think I just like the message it sends me (and me only) - I got this guitar to play it and it is a tool; don’t be afraid to manhandle it and don’t gush over its looks. Play the darn thing.
Now, having said all that, I also have that Gibson L-7c, and I have to say that I think, to me, hands down, it is the most beautiful guitar ever.
A sunburst archtop with a rounded cutaway - it doesn’t even have to try; it’s basic design just doesn’t get any more perfect, IMHO - simple and elegant. I don’t even mind the bound neck and split-parallelogram fretboard markers. It just works. But archtops are different from flattops - city elegance vs. country functionality or something - so I kind of think of the L-7c as a pretty simple archtop design…
I’m with you. My main guitar is a Les Paul Custom, which is fairly fancy-looking in stock trim, but I’ve de-blinged it as best I can - pickguard came off immediately, gold bar pickups were switched for non-covered Seymour Duncans, and I’ve been yellowing the binding with sweat and beer as best I can for 12 years. 
It’s now as workhorse as I can make it.
ETA: Oh, and to answer the OP, I have no idea, but it’s like a QWERTY keyboard; I’d be totally lost if you put something different in my hands.