Apology accepted here, cant speak for the Satman.
The JB leak is based on ICS and the kernel numbers havent changed, however they are different enough that if you update to the OTA you CANNOT go back to ICS. Whether this was a mistake as some feel or a planned early leak to test, who really knows. What I can say for myself, JB is better even in the state we have it. Hoping an "official" release will be even better.
In the ROM section we have JB based ROM's for ICS and JB ROM's for JB. The ICS ones give you an idea of how JB looks and feels but isnt as there as the ROMS made for JB. And also not sure how much development anyone wants to put into the ones for ICS. Most specifically you dont get the updated radios.
VZW did make it confusing
It's actually not the kernel (boot.img) that locks you to JB, it's a he bootloader. The bootloader in the JB leak will only allow the JB boot.img to be flashed. However, the bootloader that was flashed with ICS will obviously accommodate both. (it has to, otherwise how would the update succeed and how would you be flashing ICS fb files)
With that said, one could extract the boot.img from the JB update (with a little converting) and flash it via AP Fastboot, then boot right into recovery and flash any JB kernel based rom they want. Or, conversely, boot into AP Fastboot, flash the current ICS boot.img, enter safestrap and restore any ICS rom or even the stock system.
Tldr; kernels are compatible, flashing JB kernel isn't was makes you stuck on JB, it's the newer bootloader that is the issue.
Hope that clears some things up.
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