you can still use SDL drivers if you like and you have to run "make upgradeconf" to start using the cocoa drivers (or manually write WITH_COCOA:=1)
since SDL breaks the cocoa drivers, you can't compile with both SDL and cocoa support
Using cocoa drivers makes it easier to make universal binaries and it solves:
-FS#18 [OSX] SDL is weird in universal binaries
-FS#2 [OSX] lazy pointer crash on exit
-FS#10 [OSX] linking error when linking statically to SDL 1.2.8 (needless to explain this, but it means it should be able to compile statically with the default settings now)
-[ 1215073 ] Switching to large size out of fullscreen crashes
Using SDL drivers will still have those issues though