I think that if there already is a duplicate in the list of related questions, I will notice "$1^2+2^2+\dots+n^2$" much easier than "1^2+2^2+...+n^2" (without Mathjax) or "sum of squares".
Moreover, the MSE community is used to math in the titles. Even if you persuade non-trivial number of users that it is better to use ASCII-art instead, it will not be easy to make users to use this.
