>>>I expect it is because class files are binaries,
Class files are not binaries. Parts of the class files are pre-compiled into object code, but most of the stuff in class files is not binary at all. And at no point does VFP produce binary code.

>>> and the & command is inline, hence only works in the "interpreted" .prg files..
.prg files are no more interpreted than in the class files. The .fxp is what is executed by VFP which is also pre-compiled into object code. The "class files" (by which I assume he means .vcx/vct files) have a memo field which contains the code and a memo field which contains the object code. Classes in code are compiled into .fxp's (object code). Macro substitution works in classes as well as in .prg's.

I will restrain myself on blunt/rude issue because if I didn't I'd accuse the originator of my above quoted sections of blowing smoke out his a**.