Time. I have the time to maintain a single GUI. I do not have the time to maintain three GUIs. Of course they'll be 99% the same, but checking that this 1% difference behaves and looks fine accross systems adds a substantial amount of effort that I simply can not support. And for what exacatly? I want them to be identical accross systems, not different.
reply> And for what exacatly? I want them to be identical accross systems, not different
replyFor your users. Engineering is about designing things for the convenience of the builder, but for the convenience of the user.