Magazines don't have the cultural impact today that they did back in the 50's. Today, they are a relatively small part of a huge conglomeration of media sources. Half a century ago, they were one of the most important.
Commercial art has always been a profession with a caste system and, during the mid-20th century, there was no status higher than to be an "illustrator for the slicks". I imagine any illustrator would have loved seeing his name in the Saturday Evening Post (or any other mainstream magazine) knowing that it meant millions of Americans - not to mention hundreds of potential clients - were becoming familiar with his work.
I don't know how the Post chose which illustrators would receive story assignments... but I don't think Dom Lupo was ever among that elite group. In fact, aside from a few line drawings done for Collier's (like the ones we looked at yesterday) I have never come across any editorial art by Lupo in any mainstream magazine.
Whether this was of any importance to Lupo, we may never know -- but he seems to have been trapped on a lower rung in the world of commercial art. Destined to only see his name in the Post if it was attached to an ad he had illustrated.
You can see these illustrations at full size in my Dom Lupo Flickr set.