Have you tried copying the xampp_cli.exe
from the zip or 7zip archive file of version 1.7.3 to the installation folder of 1.7.7 and see if it works for you?SourceForge XAMPP File Repository
Might be worth a try and if it works I would like to hear back from you.
Not sure about why it has been excluded but my guess is that it was created and copyrighted by a developer that is no longer with us because he would not adhere to the XAMPP policy of open source.
Nothing to stop end users from copying from one XAMPP version to another if they choose to do so as it has a FreeBSD License.