Then again, so do the BSD tools. And of course the options are often not compatible between the two e.g. bsd sed's -l enables line buffering, gnu sed's -l specifies line-wrapping length; bsd sed's -i requires an extension (empty for no backup) while gnu sed's does not.

POSIX sed supports exactly 3 options (-n, -e and -f), the latest FreeBSD sed supports 10 (adding -E, -a, -I, -i, -l, -r and -u — the last two being GNUism compatibility options not necessarily available on older versions, they are not on my OSX machine) and GNU sed supports 9 short and an additional 4 long options. And that's not counting the extensions to the sed command set.