This allows you to go forward or back in 10 sec jumps (which you can hit repeatedly and VERY quickly), in addition to FF or REW. Very frequently I need to go back and listen to some dialog a second time, and this ability is an absolute pleasure in these situations, while Apple's skip back is unusable to me. It's personal, of course, but for me, this one feature makes an enormous and overriding difference.
Actually it is is possible to have seperate buttons by using the "learn remote" feature with any third party IR remote.