Unfortunately enough people have older CPUs that we still have to support x87 code generation; its just not used in the binary packages, you have to build the source to get it.
Factor uses ahead of time compilation. When you load a source file at the REPL, all definitions in it are compiled immediately, and compiled code is saved in the image. So when you download a pre-built binary package, all the code has already been compiled so auto-detection is not an option.
There are pros and cons to both compiling at load time or run time; one of the disadvantages of the former is less flexibility when it comes to using CPU-specific features.
