In my opinion, they went to a smooth nut for looks. Most people know that Savages shoot well out of the box. But some object to the looks of the "ugly" nut.
If Savage were really doing it to limit liability they would put smooth nuts on the Stevens 200 and "Edge" rifles.
If all else fails, you can use a Marlin XL or XS nut. Same grooves and same thread.
BTW...This isn't the first time Savage used smooth barrel nuts. I had a long action J rifle from the mid-70's that had a smooth nut.