I dont get it, so most recordings are done in mono, then edited to be dual mono (giving the illusion of stereo)? or is everyone expected to use two mics to get stereo?
I wouldn't say most recordings are done in mono. Also, just editing to be "dual mono" as you say does NOT give the illusion of stereo, it's just the same signal coming out of both L and R.
However, getting at the main point... Most formats, this includes WAV and MP3, have a "mono" format that can be used. This is preferrable for true mono recordings because the file is half the size. Pretty much any player at that point should recognize that it is a mono recording, and then it will play the mono signal through both channels on playback. However, the file has to be truely saved as a "mono" file for this to work. If it is a stereo file with only one channel having audio, then it'll play back that way. So, personally, if I was going to record in mono, I wouldn't worry too much about how you set it up physically when recording. I mean if your recorder can do true mono, then do it that way because it'll save you steps in post and produce a smaller file at the time of aquisition. But if your recorder can only record stereo (say an H120 for example), just record both channels in stereo like always, knowing that only one channel will actually have a signal on it, then in post, just convert the stereo file to a true mono file (the software will ask you which channel to "keep" somehow, and that's it. You'll have one file, that is half the size, and when played back, it'll play through both speakers.
That said, there is one advantage to routing the one mic to both channels during acquisition, and that is this. You can run one channel pretty "hot" and let the other channel have a little more headroom on the levels. Then in post, you can pick which one you want to use for the resulting final mono file. If the hot channel made it through without clipping, great, use it, if it didn't then use the other channel normalized instead.