I don't think it's anything to do with being kind or knowing what you are doing. In each case, they looked at my boarding pass and said, yes, I was entitled to use the Sky Priority line. That was when I asked about it, the first few times, then I stopped asking. Always worked.
One useful thing that I found as Silver is that when you are travelling other SkyTeam airlines they treat you simply as elite, no matter whether you're Gold, Silver or Platinum (except for lounge access). So that gives you a good placing when it comes to upgrades on overbooked flights, which happened to me on quite a few China Southern flights. Aeroflot don't seem to care one tiny little bit about it, although to get Silver with SU you need 25 flights or 50,000 miles if I remember correctly. No wonder there isn't a humming Aeroflot forum here.