not all of them start off how you would imagine. Logisticsguy had 2 fully colored males (no white chins or faces) lose all of their color and turn white. A couple more males from that same spawn turned into white fish with butterfly markings, one of those ended up losing all but one spot of black. There's definitely marble in the bloodlines, the dam is a koi (which is a form of marble), but they didn't start off looking that way. It's the "jumping gene" for a reason.
On the other hand, it's like the mustard gas, and dragonscale, the terms get thrown around and not everyone is entirely sure what either description really means. That get compounded when different breeders or sellers call them by different names, instead of agreeing on what makes this fish fit into this category.
There is an obvious progression in betta coloration marbled or not. One of my males is turning dark blue, and he was a turquoise when I got him two months ago. He's not gaining any white, so that's just his color finally settling in.
My koi marble, though. Went from this (Oct 2012):
and as of now, looks like this (March 2013):
with a lot of those changes occurring within 2 weeks to a month of the last one.
He DOES have the white chin of the colored marble. (the last picture shows that very dramatically)
In summary, you're very right, it does get thrown around a lot, but there are less well-known varieties and genes that would explain white faces, spots, or color changes that the hobbyist really doesn't know about (like me, I didn't know anything about marbles until I got here), and assigning a name to it that we hear frequently, makes sense of it all. Also, there's not always a way of knowing if your fish is a marble, or simply white on the head, until it does what my Mushu did, and change color.
I'm by no means a marble expert, but that's how I see the misuse of variety names. If it really bothers you, the best option is to calmly and constructively correct misinformation when it crops up, and hope it sticks.
By the way, thank you for the articles, I always get my colors/patterns confused.