The syntactical building blocks might be similar but the execution model differs. While you could obviously achieve any sort of term evaluation with a metainter

The syntactical building blocks might be similar but the execution model differs. While you could obviously achieve any sort of term evaluation with a metainterpreter, the TRS in Mathematica offers a rather smart rewriting system. It can easily express things like associative and commutative operators (esp. useful if you have a pattern that matches on a use of that operator), and alternate evaluation orders (outside-in, mixed, lazy, held, &c). These are hard to trivially implement w/o very different kind of interpreter. In this sense, most Lisp implementations pick a static evaluation strategy and leave implementing alternatives to a metainterpreter, which isn't exactly what's happening in Mathematica.