After much investigations from Alex and I, we concluded that the 3.73 firmware is fully identical to the 3.72 firmware, the only thing that changed were the module versions and the index.dat/version.txt that display the firmware version. ALL the kernel and vsh modules are the same, so are the rco files.
As you know this does not really make sense and we have yet to find out why sony issued a new firmware revision when nothing was changed. Perhaps there may be some flaw in the updater itself that may explain this move, I don't think we will ever know for sure.
Also this the part when some "coder" gets greeted by noobs because of being so "fast" to port "his" custom firmware to 3.73 while nothing at all changed from its previous 3.72 version. I will let you all figure out who that might be...
UPDATE: lflash_fatfmt seem to have changed a bit (over 20 different bytes) but that's all we could find, no critical change and certainly does not need ANY patches to be modified/updated in any way to run a custom firmware, perhaps the bugfix is there (we are not sure of that yet, we are curently taking a closer look at the module to be sure)