In a way I understand why Legendaries are restricted from transmogrification, if masses of people are running around with them it does kind of cheapen them as a whole but I'm not entirely sure this would happen if they were allowed. Personally I wouldn't use a Legendary just for the sake of it, I may use one for a while if it happened to look good with the gear I'm currently wearing though.
If you were able to Transmog Legendary weapons, would you actualy do so?
To be clear, I meant change the looks of your Epic/Blue/Green weapons into that of Legendaries, not change the Legendary into something else