i think you're right that the "essense" is not lisp. Mathematica is more abstract than lisp, and it has lisp-like features built on top of it. that said, the analogy can be useful because things like "macros" are completely natural to the language:

    In[1]:= FullForm[a + b]
    Out[1]= Plus[a, b]

    In[2]:= a + b /. Plus -> Times
    Out[2]= a b