Action Comics debuted in 1938 along with Superman, who first appeared in Action Comics #1. To paraphrase from Wikipedia's entry on Action Comics:
Originally, Action Comics was an anthology title featuring a number of other stories in addition to the Superman story...Gradually, the size of the issues was decreased as the publisher was reluctant to raise the cover price from the original 10 cents, so there were fewer stories. For a while, Congo Bill and Tommy Tomorrow were the two features in addition to Superman, but soon after the introduction of Supergirl in issue #252 (May 1959) the non-Superman-related strips were crowded out of Action altogether. Since then, it has generally been an all-Superman comic, though other backup stories such as the Human Target occasionally appear.
Superman's self-titled series has had a slightly more involved history. It debuted in 1939 and was solely dedicated to Superman. Its entry on the Comic Book Database states:
Nevertheless, it is clearly the first wholly American-made single-character book of the 20th century. It is also the first single-character book featuring a superhero. It's the book which proved to the modern American comics industry that people would follow a character, as opposed to a genre.
Superman was renamed to Adventures of Superman in 1987 and kept the same numbering. The name then reverted back to Superman in 2006.
As for the new Action Comics #1 and Superman #1, Tor's Reader's Guide to the New DC 52 states the following:
- Action Comics #1 by Grant Morrison and Rags Morales tells
Superman's backstory and is set in the past of the new DC Universe.
The initial press release, along with that cover image of a working class superhero, tells us that this relaunch explores a Superman who “defends a world that doesn’t trust their first Super Hero.” Unlike most of the other fall #1 issues, this one seemingly takes place in the early days of the DCU, re-establishing a new timeline for the introduction of the superheroes into the modern universe.
- Superman #1 by George Perez and Jesus Merino is set in the present of the new DC Universe.
There doesn’t seem to be any high-concept reimagining of the character here. This one seems to be generic Superman. It doesn’t seem to be all that different from what Perez did when he briefly wrote and drew (or provided plots or layouts or all of the above) Action Comics and Adventures of Superman in the late 1980s/early 1990s.
Similar to Superman, Batman debuted first in Detective Comics. Unlike Superman, who first appeared in the first issue of Action, Batman didn't appear in Detective until issue #27. For a while it was an anthology series, but it eventually became solely devoted to Batman and the Batman family of characters (not clear on when the shift took place).
Batman got his own comic with Batman #1 in 1940.
As for the new Detective Comics #1 and Batman #1, Tor's guide states:
And what we know about the opening story arc sounds run-of-the-mill. It’s Batman vs. a serial killer (someone calling himself or herself “The Gotham Ripper”). And Bruce Wayne possibly involved with a new love interest. It’s boilerplate Batman. Batman 101. The concept and characters of this series aren’t likely to be surprising. The series may end up focusing a bit more on the “detective” aspect of its title than its other Bat-centric peers.
- Batman #1 by Scott Snyder and Greg Capullo essentially continues Snyder's acclaimed run on the title, which has focused on more psychologically thrilling and horror-centric themes.
This will be the straight-ahead, no-nonsense Batman. He fights bad guys. He’s smart. He’s tough. He might even have a dry sense of humor. But he won’t be blasting off into space any time soon, and he won’t be speaking to himself in the third person while grunting out haikus on vengeance.