i guess because the dimples aren't placed in a specific position relative to the threads, hence the dots don't always give a good indication of how far backed out a tailswitch is. for the LOTCs, this resulted in different surefires having different amounts of travel in the switch when the dimples were lined up.
for example, from the position where the dots line up on my C2, three quarters more of a complete turn is required to turn it on whereas on my M3, only one quarter more of a complete turn is required to turn it on. an M2 i had required exactly half a turn to turn it on from the position where the dots lined up.
for the LOTCs, this wasn't such a big issue because you could always just use the dots as in indication of how much you've twisted the tailcap so you can set a specific amount of travel in the switch. for example, with the regular Z41 tailcaps i've found half a turn is the most ideal, with anything less being too sensitive and anything more requiring too much tension.
i get the idea the clickie tailswitches have to be tightened fully for the clickie to work, so if that is the case then the dots or dimples wouldn't serve much of a purpose if they didn't line up on every unit when the clicke is fully tightened. (someone correct me about this if i'm wrong though)