Estimating the standard deviation of a distribution requires to choose a distance.
Any of the following distance can be used:
$d_{n}((X)_{i=1..I},\mu)=(\sum \left | X-\mu \right |^n)^{1/n}$$$d_n((X)_{i=1,\ldots,I},\mu)=\left(\sum | X-\mu|^n\right)^{1/n}$$
We usually use the natural euclidean distance (n=2$n=2$), which is the one everybody uses in daily life.
The distance that you propose is the one with $n=1$.
Both are good candidates but they are different.
One could decide to use $n=3$ as well.
I am not sure that you will like my answer, my point contrary to others is not to demonstrate that $n=2$ is better. I think that if you want to estimate the standard deviation of a distribution, you can absolutely use a different distance.