TeX used to have numerous unique features: fairly good fonts; automatic hyphenation, which makes it feasible to lay out text with full justification; support fo

TeX used to have numerous unique features: fairly good fonts; automatic hyphenation, which makes it feasible to lay out text with full justification; support for non-English Latin characters, etc. The rest of the world has caught up with these. IMO the ways in which it is still special are: (1) good math typography; (2) integration with automated bibliography systems; (3) easily generatable by other tools. (Lots of things that eventually turn into HTML hit #3, but not lots of things that eventually turn into really good-looking PDFs do.) These points certainly aren't important in all cases ... but for what it's worth, arxiv.org hosts more than a million scientific papers, the vast majority of which are written in TeX.