Intertextuality in sci-fi?

I have slowly been reading my way through John Ringo's multiverse for the past two years or so. After reading Robert Heinlein's Starship Troopers last summer, I realized how much he influenced Ringo's writing. I'm talking stuff like mechanized full-body combat armor, dropping from a ship in orbit to take out an infestation of "demons," and other stuff I can't think of right now.