Its pretty much passed down to you...and from what your taught,you adapt to what works for you.Toney and Floyds defense differs slightly.If you notice Floyd relies a lot on his ability to see punches coming(without this, he'd get KO'd by hooks all day).Toneys is fairly basic because he relies more on focusing on a few punches to block,etc...
Its not widely taught because it wont work in the Amateur ranks...and not to many people change their whole style of boxing right away.