bazzlad said:
Yeah but most Amps have LINE OUTS, which feed the distorted sounds straight to the desk etc....
True, BUT those line outs are one of the following:
a) direct out from the preamp section, totally ignoring the tonal characteristics of the power amp and speaker, or
b) emulated line out, which does its best to emulate the power amp and speaker.
I have a Tech21 Trademark 60 with a SansAmp line out, which is one of the best emulations I've ever heard on a line out. BUT I can still tell the difference between the line out and the speaker sound. Not to say that one is better than the other, they are just different.
As has been mentioned before, mic'ing an amp brings in the characteristics of the power amp section, the speaker, vibrations of the amp chassis, room dynamics, mic response and character, differences in mic placement, and character of the mic preamp.
Use whatever you like the sound of, but don't ever make the mistake of saying that they are the same.