If by "bushcraft knife" one means something like the traditional Scandinavian knives such as puukkos, or the Ray Mears Woodlore and pals kind of knives that largely imitate such Scandinavian designs with minor changes like thicker blade stock and such... then the special thing about them is that they actually work extremely well for working wood and allow for a great variety of different grips for different situations and tasks (since there aren't any bothersome finger guards and similar obstructions in the way). The original Scandinavian designs from which this type of bushcraft knife is derived from was intended to be an effective, simple general use and woodworking tool that, combined with an axe, could basically handle all a man might expect to have to do in the Scandinavian wilderness. Compared to modern day tactical knives for example, the difference in woodworking performance is very great indeed.
Of course, sometimes "bushcraft knife" is used to refer to "any knife you might feel like taking outdoors to do... well, bushcrafty thingies."

In that case, there isn't anything particularly special about them, since they can be any knife.
To get back to the Scandinavian style bushcraft knife, though, they are very different knives compared to American tacticals like Busses. I'm a happy owner and user of a number of Busse knives, and I like every single one I've got and intend to keep them. But they are built for very different use, really, and with an entirely different philosophy. Basically, it's like comparing a surgeon's scalpel to a butcher's meat cleaver. Yeah, both are supposed to cut "meat", but there are jobs that you really can't easily do with a meat cleaver that you can do with the scalpel, and obviously, vice versa.
Busses are "hard use" type of blades, designed with the philosophy that you can cut stuff with them, but also do a hell of a lot of other things like chop, pry, bash and generally whack the crap out of things with. Some of them are large enough to be meant to replace an axe (the Battle Mistress comes to mind here

). Since they're meant to be used for "all kinds of stuff" and the tactical knife philosophy in general requires putting guards on knives, Busses come with guards. The Scandinavian style bushcraft knives, are meant for far finer work than Busses. They're not tools for chopping or such - that's what the axe is for. They're intended to be used for "fine" cutting: for some examples, things like building traps, carving eating utensils and other tools, skinning something you just killed, cleaning fish, some tasks in shelter building and firecraft. The axe is used for larger jobs that require chopping power and toughness. They're tools intended to be used with
skill, choosing the right grip for the task. If you're going to stab, support your grip properly by the butt of the knife, so your fingers don't slide - use the palm of your hand or at the very least your thumb. If you're going to be stabbing because you're fighting... well, the saying goes that the knife is used to keep the other guy in check until you can get to your axe, and that's when the fighting really starts - with the axe.

In all my years of knife use, I've never had one of those almost mystical accidents some folks speak of, where the hand just somehow slides right onto the blade during use. It's a knife - it's supposed to be used with care, not recklessly. Men do as they've been taught to do. If one grows up using knives that don't have guards, there isn't going to be a problem - you'll learn the grips you're meant to use, and you'll find using a knife with a guard even a bit difficult at times since it limits those grips. If one grows up using knives with guards, then it's easy to think that guardless knives are inherently somehow dangerous as if your hand could just slip all on its own onto the blade. It's kind of a cultural thing, I suppose.
I will certainly recommend giving a try to one of these knives. A cheapo Mora will show some of the performance that is there. Quite frankly, a "marketing fad" the bushcraft knife is not. Perhaps the word "bushcraft knife" itself is a fad, it sure sounds like one. But the knives themselves, referring to Scandinavian style knives, certainly aren't a fad. The design is extremely old and proven. It worked then, it works still.
I'm sure I read (Maybe in Kochanski's book) that a good mora was tested by hammering it into a tree and standing on the handle to see if it could support your weight.
Anybody else read that somewhere?
Yeah. I really wouldn't recommend doing that with a Mora. Or any knife for that matter. Moras are "tough" as far as Scandinavian knives go, but they're not meant to be extremely tough. Nor should you try to stand on them after one's been hammered to a tree. Sure, sometimes it will take it. And sometimes, it won't, and there's a good chance someone's gonna get hurt.