Well we're talking about bonding metals here at a molecular level; of course it's microscopic!
Sorry scorrpio. I just couldn't resist. You are absolutely right, of course, that tin works just as well. But you said it yourself - where is the magic in that?
Truly, by the time a tinned contact is worn out, the "gold" (or 2 carat alloy thereof) has worn completely away. What remains as true, I suppose, is that it is good to have contacts with good conductance, some resistance to corrosion, and just a tich of malleability (and saying all that just now, it's hard to imagine anything much better than a good tin-formulation. But gold's still prettier.)
The bottom line is that, for your conductor, copper is (speaking practically) as good as you'll get (gold? silver? Get real your highness. But tin? Wouldn't have the durability - it doesn't form the durable, elongated crystals that drawn copper will). As an alloy, copper may have the softness that you want (you want your points of contact to "become one," at least a little bit), but it's just too darned easy to oxidize. So you coat it with something that's about as soft, promotes the free flow of electrons about as well, but turns up it's nose at oxygen a little bit better (the o2 will make it too hard and brittle to deform properly, and locks up the electrons so that they have to leap across, rather than flow through). Beyond those realities (and built around them, I must sadly say), is a boatload of marketing bullcrap.
And thaths, the trutthhh. (D'yall remember Edith Anne? How do you suppose you spell what she said? Hmm, question for a different forum, I suppose.)