Extended travel Coilover vs 3/8" strut spacer on regular coilover

Hi everyone, this might be discussed before but I could find a thread through my search. So I want to bring up a discussion about this. I'm not sure if my reasoning is correct so I want to hear your opinion.

ICON and some other coilovers offers extended travel coilovers. To my understanding these coilovers are around 0.5" longer than regular ones when fully extended, which give you the extra almost 1" down travel. They achieve this by using a different internal bumpstop on the top.

If only concerning about down travel, this would be equivalent to putting a thin 0.5" strut spacer ontop of a regular travel coilover (e.g. ICON stage 1, Toytec etc). Wheelers offroad offers 3/8" spacers which is close to 0.5". The only potential risk i see is the shock piston taking the hit instead of the frame mounted bump stop when bottoming out. Yet I doubt those regular shocks don't have that 3/8" ~ 0.5" marginal uptravel. If we don't run into this problem, then we don't lose any uptravel, hence achieving the same as an extended travel coilover.

I guess I must missed something otherwise all manufacturers would build in that tiny amout of height. But can't figure out why not. Thanks in advance.

PS: all above is assumed running after market UCAs.