Clarification for microstepping requirement

Hey all:

I read the great FAQ's on this site regarding steppers and how they work and
microstepping. Very inciteful and I think I even understand how they do it.
What I can't quite figure out is why it is required. In one of the FAQ's it
says the primary purpose for microstepping is to eliminate the jerkyness
between steps. However, when I do the math on my proposed set up I come up
with a movement of the axis per step that is so small I can't consider it to
be 'jerky'. Therefore I am afraid I either didn't understand what I read
well enough or I'm missing something. My math is below and I welcome
comments.

System statistics:
Lead screw with 10 TPI
1:2 gearing between motor and lead screw
motor with 200 steps/revolution

My math:
Every turn of the lead screw gear produces .1 inches of travel.
Every turn of the motor gear produces .05 inches of travel
Motor has 200 steps per turn of the motor so every one step would produce
.05/200 inches of travel

In summary .00025 inches of travel per full step seems like a very small
amount of movement. So why would I need to divide that by 10 for a
microstepping drive?

Thanks in advance,
Eric Q.