--throw-keyid and -R options

[privacy.at Anonymous Remailer]

Is there any difference between the effects of following commands?

gpg -e -R alice -R bob file

gpg -e -r alice -r bob --throw-keyid file


And when I abbreviate --throw-keyid to --throw or --throw-keyi even, I
get the error:

gpg: Option "--throw-key" is ambiguous


There is nothing else that starts with the string "throw" so why?