In practice I tend to think of Scheme as quasi-standardized, in the sense that there is a standard core, but it's difficult to stay within it. Whereas with standards like C99, Fortran 90, or ANSI CL, it's quite common for people to write nontrivial standards-conforming programs that you can expect to run unmodified across implementations. Culturally the Common Lisp community also seems more interested in maintaining portability even when leaving the confines of the official standard, through the heavy use of compatibility layers like Bordeaux-Threads. The Scheme approach seems to be to just target a specific implementation, and share functionality across them on a case-by-case basis by porting libraries (which is sometimes trivial, and sometimes more involved). Hence CL has Quicklisp, while Scheme has a package repository per system.