It's certainly true that Lisp's super-simple syntax makes it much easier to have a powerful macro system. Dylan macros are like Scheme's hygienic macros, based on pattern-matching and not as flexible as CL's fully general code-generating macros -- but still pretty powerful. (And there's an unofficial procedural macro system too, which I haven't looked at but I understand gives you CL-like power without too much pain.)
Counterexample: macros in Dylan (http://www.opendylan.org/books/dpg/db_329.html).
It's certainly true that Lisp's super-simple syntax makes it much easier to have a powerful macro system. Dylan macros are like Scheme's hygienic macros, based on pattern-matching and not as flexible as CL's fully general code-generating macros -- but still pretty powerful. (And there's an unofficial procedural macro system too, which I haven't looked at but I understand gives you CL-like power without too much pain.)