sort is implemented in a way that parses these in the way you expect.
See also here:
- Sometimes options and their arguments are run together, sometimes separated by whitespace, and sometimes by a character, typically : or =. Thus "Prog -fFilename", "Prog -f Filename", "Prog -f:Filename", "Prog -f=Filename".
- Some programs allow single-character options to be combined; others do not. The switch "-fA" may mean the same as "-f -A", or it may be incorrect, or it may even be a valid but different parameter.
This looks like a combination of both (works without whitespace, and combination of single-character options).
They are simply different programs whose argument parsing is implemented differently.
coreutils 8.13, compare the following::
src/sort.c line 4315, invoking the special integer parsing function
parse_field_count, that returns with the first invalid character (i.e. once the number value is finished and the next option starts): That's why
sort can handle your arguments.
src/cut.c, line 803 ff., simply using the regular
getopt behavior of interpreting everything until the next white space as parameter to the current option.