The question is what standard allows this. Some Unix implementation allows the extra formats in inet_aton. This is visible with Perl and web browsers. Most people would consider the short-form addresses to be errors and only four decimal components to be valid addresses. It makes sense to reject or ignore long form addresses to keep from confusing people or other software.
It is possible to restrict the range of numbers with a more detail regular expression:
/^([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-5][0-9])$/