No, but it supports LaTeX math mode commands, such as \frac, that are not in plain TeX (in plain TeX $1 + \frac{a+b}{c+d}$ is written $1 + {{a+b} \over {c+d}}$

No, but it supports LaTeX math mode commands, such as \frac, that are not in plain TeX (in plain TeX $1 + \frac{a+b}{c+d}$ is written $1 + {{a+b} \over {c+d}}$ --but you might be able to omit one set of braces). I don't see any reason for people to avoid the LaTeX additions to mathmode.