I think my thing is I like the black color next to the ivory/white of the dress. I mean when it comes down to it we are all snazzied up (i.e. not wearing any old off the rack dress from your local department store) so I think the guys should be too!
Black just bumps things up a notch, even if it is a linen suit or whatever. I am asking guests to dress "beach chic" so khakis and linen stuff is ok for them, but I don't want my FI to blend in with the guests!!!!
I did not choose a DW because I wanted a casual environment, I wanted an environment that was beautiful and honeymoon wrapped up in one!
I dunno, that's just me...