The examples you gave were famous because they did famous things. Custer was a newsmaking young officer during the Civil War and then died in one of the most famous battles in American History. Lee and Jackson were famous because they won battles, just as Longstreet, Sheridan, and Sherman were famous. They got in the papers. We still do this, though. We followed MacArthur during Korea just as we did Ike, Patton, and Monty during World War II. We knew who Abrams and Westmoreland were because they were in the news regarding Vietnam. Powell and Schwarzkopf became celebrities during the first Gulf War and Powell made a political career out of it. There is nothing new to this practice.

Someone please correct me if I am incorrect or if you have a better explanation. Its three a.m. and I finally found a question that I felt I could adequately answer.

The way my dual credit history class professor put it, celebrities as we know them did not come into the spotlight until the early 20th century, due to the invention of different types of entertainment and mediums of relaying information (i.e. the radio). Before that, wars and conflicts (of any kind, really) were what made the news (usually passed by word of mouth). Because of this, high military figures were considered celebrities due to the fact that there just weren't many other famous public figures for people to be familiar with (same with politicians). This is super notable with the elections of President Jackson and Taylor (to name a couple) who were famous military heros for their time periods, compared to say, President Reagan who was originally an actor on televison.