how the bytes ordered in mpc8313

I have mpc83xx,

I saw that I need to use swab32 to any read\write operation from registers,

I don't understand why I need it?

Do I need it for all registers?

Why in the mpc8313 reference in registers description some bits look like
31,30,29,.,3,2,1,0

And some: 0,1,2,3.,30,31

Is it just mistake? Or some registers are different then other?