There used to be TeX/LaTeX support, which is what you would use to create such equations. Support for it got taken out with the move to the new system. I agreed that it was not the most commonly used feature, but when you need it, it is certainly very nice to have.
It would be nice to have some sort of MathML / Mathjax / LaTeX support for writing equations.
Are you talking about posting here in DW or just in general? I'm also assuming you're referring to web pages?
While not so nice within your post, looks fine if I click on the small thumbnail at the bottom of your post because the image is displayed in a new page. You may want to try it again, but rather than exporting as a gif, try png as I did in this post..