Solaris, HP-UX and OpenServer have not.
AIX is weird:
> -r Searches directories recursively. By default, links to directories are followed.
> -R Searches directories recursively. By default, links to directories are not followed.
Hence, only lubutu's comment ("-R is the recursion flag for ls, cp, rm, etc") is true, while _delirium ("-R is the POSIX-standard flag for recursive grep") is wrong, which means AIX is free to do whatever it wants with both the -r and the -R flags.