Are we really going to have that many more pathogens on our knuckles than on our elbows? - less but not even close to zero. Go for handrails or door handles and those knuckles will eventually meet door or wall, particularly on a moving bus. Especially with UK roads, don't get me started on potholes! You try descending stairs in a moving switchback!

whereas handshakes often connote a desire to dominate. true but then we handshake to show our swords are enscabarded (?) or at least not in our hands, even in the dark. Well I do, don't you?