My guess on AT only on the top trim line is because most people do not want MT especially those inclined to buy more luxury (as it were on the X) items on their vehicles.

If you do not plan on spending much time off road get the S trim, in 4X4. You don't need the locker if you are not pushing the envelope some. But 4X4 comes in handy quite often and you will be amazed at what the X can do even without the locker.

Get an X! Join the fun!