Jon you are absolutely correct, for some reason, the pictures I "thought" I saw had the notch narrower than the foot of the rail. Going back and looking carefully shows that the foot indeed sits in the milled slot.. that should completely solve the "skewing" issue, although you want to be sure your rail foot matches the slot.
I'd swear the first pictures I looked at did not have the groove machined with square sides, but more looking like a mild depression... I must not have looked carefully.
Ahhh... this picture below is what I saw, and it did not appear the milled area allowed the rail to sit down inside:
The "far side" of the slot looks like a curved surface.. but other pictures show a nice square edged slot milled in and the rail sitting in their nicely.
All that said, trying to "pull in" the ends of rails on a curve would be a pain, you'd probably need to twist the end of the rail to go into the groove.
I'm more than happy with SplitJaws and I really do not want 4 screw heads staring up at me... these are the tradeoffs, clearly easier to get to the screws if they point up.
Greg