Consider an app designed by Mac people that has been ported to Windows,
and a Windows app that has been ported to Mac OS. Windows ports do not
please Mac users, or vice versa. This is because a good port of an
application doesn't just transport the code of a program, it translates
the *philosophy* of the program to fit in with the native system. It's
almost a rewrite.
If you built, say, Alex's Terminal app on an OS X box, you're not now
running an OS X application -- you're running a GNUstep application on OS
X. In the same way, if you were able to get and build Safari on a GNUstep
system running under Linux, it's still a Mac app that happens to be
running on an OS other than Apple's. So its metaphors will be different,
the location of the "widgets" won't be what we would expect them to be,
and so on.