Here's the part I don't get about following the grain, figured might as well hash it all out on this thread.
Growing up in Illinois, Osage is usally a throw-away junk wood, it's only purpose being of hedgerows and such. So...I've had the pleasure of knowing how heavy this stuff is prior to getting into this hobby. Although I haven't made an osage selfbow yet, I would think that splitting that sucker by hand would be a TREMENDOUS amount of effort for no more than you really get out it.
I would think that if the grain waves more than 3 or 4" vertically, it wouldn't be much use for a bow anyhow, and certainly not "average" from what I've seen in pictures, like the one George provided the link to - it's probably 2" of wave.
With that being said, why not just cut into stave sections using more "mechanical methods" (chainsaw, bandsaw, take it to a lumber shop), and then just follow the grain on the center line of the bow. As long as the stave is 4" wide or so, I would think you could still follow it with the centerline of the bow, especially as you get down to the narrower tips.
So I guess the real question is here, what I'm a missing?