Among the many remarkable things about the revival of interest in old school gaming over the last few years is the revival of interest in the 1974 edition of Dungeons & Dragons. To my mind, that's an amazing thing, given that, when I entered the hobby -- a mere five years after the publication of OD&D -- hardly anyone played it anymore. The older guys talked about, of course, but they didn't play it, at least not that I ever saw. Most of them had "moved on" to AD&D or other games. That's why it'd be many years before I had the chance to peruse those little brown books for myself and see the seeds from which this hobby grew.
If, as lots of gamers have been doing recently, you take a look at OD&D, there are lots of little oddities -- no pun intended -- that you'll notice. One of the most intriguing is the influence science fantasy had over the early game. Gary Gygax's "forward" [sic] to the game specifically puts the Martian stories of Edgar Rice Burroughs on the same footing as Howard's Conan and Leiber's Fafhrd and the Gray Mouser. I think only Tolkien rivals Burroughs in terms of the number of references in the text to his specific creations (and, of course, those references to Tolkien were eventually eliminated in later printings). Heck, there's a several optional encounter sub-tables that are intended to replicate Barsoom.
I'm not alone in noticing this. In fact, I'd say that one of the biggest fruits of the recent study of OD&D has been a wide embrace of science fantasy as being every bit as influential over the early hobby as fantasy. You need only look around the blogs, forums, and even OSR publishers to see the truth of this. From my own perspective, I'm deeply grateful for this myself, since, as a younger player, I had a very narrow definition of "fantasy" and would have been appalled by OD&D's mention of robots and androids as potential "monsters," never mind Supplement II's full-throated acceptance of alien visitors from another world.
I won't go so far as to say that science fantasy is alien -- there I go inadvertently punning again -- to AD&D, but I do think it's fair to say that OD&D is so loose and open-ended that it's much more amenable to it. AD&D had Expedition to the Barrier Peaks, of course, but I'm not sure that module defines AD&D in the same way that The Temple of the Frog defined OD&D, for good and for bad. One might reasonably argue that AD&D is simply a particular implementation/interpretation of OD&D and, if so, I'd agree. But, being such, it carries with it a lot of assumptions, one of which being that science fantasy elements, if present at all, are deviations from the norm. OD&D has no such assumptions, because it barely has any assumptions at all, leaving it to each referee to decide what "works" or does not for his campaign.
Regardless of whether you agree with that last paragraph or not, I'm very happy to see the return of science fantasy to the fold of "correct" influences on one's D&D campaign. My own campaign has been improved by my own embrace of science fantasy; I know I am not the only one.