Symbolics Genera doesn't pass S-expressions (i.e. text) between processes, it passed objects. Everything runs in a single address space so this is cheap and accurate.
Also, ZetaLisp and Common Lisp have way more types than those supported by S-expressions. For example, they have real vectors/arrays, structures, and full objects.
Don't assume all of the Lisp world uses just the subset of Scheme used in the first couple chapters of SICP.
Only knowing Genera from a user perspective, I just assumed that process-to-process communication gives preference to the internal representation when it is available.
Well if at the end in your programmes you got to manipulate structured data (represented by sexps which whatever extensions), then the guts are irrelevant.
Also, ZetaLisp and Common Lisp have way more types than those supported by S-expressions. For example, they have real vectors/arrays, structures, and full objects.
Don't assume all of the Lisp world uses just the subset of Scheme used in the first couple chapters of SICP.