You guessed correctly, it's just better steel. I've seen new Low Walls in .223, and .45 Colt also.

Paul_F., my bookmark for Uberti is (You need to Login or Register to view media files and links), which appears to point to a site in Italy. The U.S. site was down some time back, when ownership of the importer was changing, and this bookmark dates to that time. A printed catalog I received several years ago from the U.S. importer also showed these Low Walls, and I recall seeing them listed then on a Canadian dealer's site.

edit: (You need to Login or Register to view media files and links) in Canada currently lists various Uberti Low Walls. Whether they are actually available is another matter, of course. The previous U.S. importer told me the factory catalogs many different rifles, but production runs can be years apart.

You might try calling Buffalo Arms (208-263-6953).  Their catalog lists Cimarron High Walls, manufactured by Uberti, and Cimarron Lo Walls, manufacturer not stated.  The catalog lists a .30-30 Lo Wall, but their web page,  (You need to Login or Register to view media files and links); , doesn't list the rifle in .30-30. 
   I have a Shuttleworth Stevens in .38-55, and its now in transit back to me with a new barrel in .30-30.  I like cartridges based on the .38-55 parent case, and also have toyed with the idea of  .25-35 and .32 Win Special barrels.  (OMG!  I do believe that the .219 Zipper also is whispering into my all-too-willing ear!).  Creeping old age may be responsible, but I've become enamored of single shots over the past two years, and if this keeps up, my black plastic bolt and gas guns may just have to leave the safe to make room for more of the oldtimers!

Tommy