Tiger ships with ship with GCC 4.0 , yeah ! great ! but the binary produced won't work with anything older than 10.3.9 :-(, GCC 4.0 is the default compiler in Tiger. When Apple introduced Panther a year and a half ago, you had to use SDK's to produce binary compatible executable with 10.2 and 10.1 systems. So we could compile but it did not work. Today we can't even compile :-( and Apple tries to enforce developers to follow it's "let those version of the OS die" strategy. Bug #292530 is the one to follow.