It sounds like you're talking down flow vs up flow "bog"
@Sisha - am I understanding correctly? Technically you are correct - in nature, the water flows over and through a bog, it isn't pumped up from the bottom. However, I think you'd find down flow bogs have their downside as well - specifically the clogging that happens at the surface.
Neither of these is truly a "natural" construction so both require some maintenance. In my case I pump "clean" water to the upflow bog because I have a negative edge that dumps water into a "down flow bog" - which is really nothing more than another form of pre-filter that has to be cleaned periodically.