Out of curiosity, why do you feel they are so usable and what do you feel they are usable for?
To be honest, they're useful as defensive knives that can be carried without any kind of permit. Think of the problem; it's only legal to carry a two-inch blade. What's the best possible design for a fighting knife with only a two-inch blade? I think this is it. Also, most of them come in handy clip-sheaths that hide anywhere yet provide instant access. That's why kayakers and rafters use them. I'm a big kayaker and I go out in the ocean quite a bit. My major worry is entanglement. One of these with a serrated edge always fits the bill. I keep a cheap stainless version clipped to my vest (I forget the make).
I have a concealed weapons permit, but in a lot of places, the average person can't get one. Also, states look for ways to deny you. I know in Georgia, a simple misdomeaner (sp??) convicion for marijuana possession prohibits you from EVER getting a weapons permit, EVER (So much for college indescretion). Got caught in a lark that turned out to be criminal tresspassing? Get in a fight with your, soon-to-be, ex-wife, slap her for the first time ever, and the police show up? Forget about ever legally being able to carry a weapon again, EVER. There are plenty of people who aren't criminals who fall under this catagory. Have you have ever been hospitalized for severe depression? Should that mean you're denied any right to effective self-protection? None of these things apply to me, that's why I'm able to write about it.
What about walking around in a strange place in a different state? It might be nice to know that the knife you carry is not only legal, but effective.
It goes without saying to check the knife laws, but 2" single-edged blades are legal almost everywhere. (I do think there are places that prohibit all fixed-blade knives. I could be wrong)