shot in the dark
here is my shot in the dark guess and the differences between the kernels.
The Redhat kernels probably go through Redhats testing with certain components and whatnot. Then when a kernel patch comes out, they decide if its worth the cost to retest the patch. If so, they put it in, and test it, then give a new kernel number.
So its really the same kernels with different patches.
thats my guess.
...And now abideth faith, hope, charity, these three; but the greatest of these is charity.