Let me start off by saying this. The android 4.3 leak the GS4 has in incomplete (it is after all a leak). It does not have any 4.3-specific goodies, it is very similar to 4.2.2. It does have a new camera, though, but the Google Edition 4.2.2's for the S4 and HTC One have this camera as well.
Samsung has also implemented SELinux in a way that it blocks root access (though strangely enough not to ADB).
EDIT: Samsung only seem to block their leaks/beta's while the releases are ok. Do you think they do this to ensure that they can't be rooted, so they can gather our reports on how they are? After all, some root-related activities may or may not affect the performance.
This is what I've concluded by reading around here and there and also based on what Chainfire has said.