I think it's a courtesy when people post that they've received their magazines. As someone who has had an issue or two lost in the mail, I think it's a good idea to know that the magazine is on the way. It provides me with an idea of when I might expect mine to arrive.
Yes, there are those that will say "Upgrade to first class." My answer to that is that not all of us can afford it. Laugh if you will, but for some of us it's the truth.
So, I'll be watching for my magazine and will happily post it's arrival...