[teddyh]

Is it not the fact that macros can be defined and, more importantly, redefined at runtime? If so, would that not mean that macros must also be expanded at runtime?

[lispm]

If you have compiled code, you have to recompile the code when you change a macro. It's not done automagically.

If you have interpreted Lisp code, then the code can use the new macro automagically.