This just isn't true. In a web browser, sure, the UI barely matters. Going through the menus in Firefox or Chrome is rare, enough so that Chrome tends to look different every time I do it.
But for real programs, the UI defines the workflow, and that should be optimized, even at the expense of familiarity. Just be sure that it actually IS better.
So yes, the quoted advice should probably be considered and possibly adopted by FireFox and maybe Chrome. But desktop software shouldn't accept it without a huge dose of salt.