I think you did not pass the Accept-Encoding header . Browsers pass it by default, and your CLI tools you must run these parameters yourself.
wget, curl (-v verbose command, /):
curl -v "http://www.abcd.org/portal/ABCPortal/private/DataDownload.action?downloadFile=&workspace.id=4180&datasetId=76999" -H "Accept-Encoding: gzip" > /tmp/yourZippedFile.gz
, , , . , HTTP-.