I'd attribue the longer lengths to the rotoscoper of the day. George wrote and always maintained 1 meter, 36" for a saber blade. Look at the orginal props for the films, there is no way they were 4 foot blades. Your eyes decieve you, don't trust them.
I think Mauls were 30" or so, Ray asked for them to be shortened quite a bit, but when he was using one blade it was 36". All of the TPM-ROTS blades are 36" standard.
As for blade length adjusting etc...thats just giving excuse to the extra knobs on the graflex and MPP...silly really, since its never been shown in the films aside from rotoscope inconsistancy. If anything the extra knobs on Vaders allows for the blade to come out of the pommel end.