This is a minor point, but I was fascinated by it, so please bear with me.
There is a brief article in the current issue of Psychology Today that deals with rejection and how to help others deal with rejection better when you are the bearer of bad news. One tip in the article was to be dressed less well than the person you are about to turn down.
This immediately made me think of Vito's meeting with Sollozo. Vito was dressed in a sports coat and slacks combo that was seemingly beneath his standards; it was certainly the most dressed down he ever was for a business meeting. (In the novel, Tom inwardly thought of his outfit that day as "peasantlike" IIRC) I never understood why he would have dressed like that for such an important meeting, but now it makes perfect sense.
Funny to still be figuring things out so long after initial viewing.
FYI, here is a link to the online site for the current issue (though the article I referred to is not available online) -
http://www.psychologytoday.com/magazine/archive/2013/09