The "arc shaped" blade tang is intentional. It's called a radiused lock face. Lots' of Kershaw/ZT frame lock knives have them, such as the 560 and the Tilt and Spyderco uses it a lot on their frame locks and linerlocks, including the Military. Strider is the main brand people associate with radiused lock faces because they used to have an extreme radius on their knives. You can do the research if you want to understand the logic and arguments behind radiused lock faces and "minimal contact" lock-up (which radiused lockup knives usually employ) versus full contact flat blade tangs, such as Chris Reeve knives. CRK has their lockup figured out and their tolerances are good enough that they can make a knife with a lock-up that mates perfectly with full contact, and then you don't really need to worry about lock wear, lock-rock, etc. But most knife makers can't make their knives that perfect, at least for their price point, so they do other things that fight lock wear and lock-rock. Good knives like Spyderco and ZT with a very mild curve to the blade tang seem to have a good happy medium where they wear slowly and have strong lockup that you shouldn't every have to worry about. You can see for yourself that the Southard has amazing lockup and should stay that way. However, even Strider changed their lockup to CRK style in the past year or so, because the extreme radius they used (even with all of the argument for it) just did not work very well for a very long time, which is why Strider ininfamous for having lock issues, especially lock-rock.
To get back on topic - I am completely in love with my Southard. I've had it on me non-stop for the past week and a half. It's just perfection and truly a knife of the year. I don't get this infatuated with most knives, especially in the price range. Knowing how much I love this thing, I would have paid a lot more for it. Just love it.
