The biggest difference for me was the consistency. With several cheaper rice cookers I've used, the rice could come out a little dry or a little soggy with no apparent cause. The Zojirushi cookers come out perfectly every time.

There are also a couple minor convenience points. Not having to soak the rice in advance(and risk forgetting about it) is helpful--the fancier cookers don't start cooking immediately, but soak the rice for you first. The timer can also be convenient--if you want rice at a certain time but won't be at home an hour in advance to get it started, you can just set the timer and go.