For what it's worth, I wondered about this too. 10 days doesn't seem like something that should be considered late to me. Heck, I had a trade recently, here on SCA, that took over two weeks after I sent for it to arrive and I got my end in less than a week from the same trade. So, as you said, nobody really has any control over the USPS. Assuming the cards were sent in a timely manner, at that point it's out of our hands.
That said, this is one of the reasons why I wanted to make these transaction details/threads publicly available to everyone. Some folks might see your star rating ding and wonder why your rating has a blemish. On SCA, they don't have to look too far to be able to find out exactly what happened.
