Skimming this thread there does seem to be some potential for someone reading it to be confused between the audio quality of the devices under discussion when used variously with internal mics, external mics directly connected to a recorder's mic input socket, and external mics connected via a preamp to a line input socket.
Every recorder has different strengths and weaknesses in each of these departments, not always just in respect of self noise. For instance, if you use a Zoom H2 (or H1 or H2N) built in mics for most of your recordings, and you switch to a Sony M10, you will probably be disappointed (the Sony's mics give a close-to-mono sound, even though they are low on self noise). If comparing a Zoom H2 mic input to a Sony M10 mic input, you'll probably be delighted with the latter (but the H2N is no disaster on the other hand). Etc etc.