[bradart]

The way Z4root operates is that it leverages an exploit in the base code of the android operating system allowing you to give certain applications root permissions. Not only is this reversible via a software switch, but it is turned off as soon as the device is turned off.

The process of flashing a kernel is done through the recovery console, which is on a different partition of the phone's memory. Z4root will not allow you access to this recovery partition.

It is easier to understand if you know how rom and kernel flashing works:

There are 3 main partitions on an android phone (for simplicity's sake):
1.System
2.Data
3.Recovery

These all store data independently of each other but can still interact and exchange data, provided the correct permissions are in place.

When flashing a rom, it cannot be done while the phone is booted. This is because you would essentially be deleting and adding code while the code is currently in use which, obviously, is not possible. Enter the recovery partition. What the recovery partition exists for is simple: It is there solely to provide recovery (obviously) and simple system update operations to the system and data partitions. Like I said, provided the permissions are all there, the recovery console can interact and modify data on the other partitions freely. Since you are booted into recovery, the code you are deleting and replacing is not in use and, therefore, fair game to be modified.

In addition to that, Z4root does not add busybox to the system bin, so you wouldn't have the proper commands to modify your recovery image.

Hope that helps.

Also, for FURTHER future reference, and I can't stress this enough,

BEING S-ON OR S-OFF HAS ABSOLUTELY NO BEARING ON WHETHER OR NOT YOU CAN FLASH ROMS OR KERNELS, AND IT NEVER WILL.

Thank you.

Edit: I'm going to clarify that last yelling part:

S-ON and S-OFF are indicators of the key in hboot (yet another partition on the phone that was not relevant to speak of in my first rant about recovery consoles) that allow you to flash unsigned images.
Now, I can understand why it would SOUND like that has something to do with rom flashing but it, in fact, does not. There is a very specific instance or two in which being S-OFF can be employed. It allows you to flash a PC36IMG.zip that has not been signed with HTC's developer keys, allowing you to flash non-stock recovery and rom images in .IMG format. If you are rooted, you can choose to leave your phone S-ON and it will have no effect on your ability to flash roms or access the recovery console. It is simply a tool you can use to re-gain root access should an unrootable update make its way onto your phone.

Thanks again.