That doesn't make sense.
As I downloaded from Steam, I don't have a physical disc, or Starforce. According to every source I can find, Starforce hasn't been included in SH3 for some time. That's one reason I finally bought SH3. I'm certainly not going to buy it a second time.
I can find no evidence of Starforce being present on my system. The official Starforce removal tool (linked to in this forum about a year ago, here:
http://www.subsim.com/radioroom/showthread.php?t=160118), does not detect any Starforce drivers in use on my system, nor do I have any of the registry entries associated with Starforce.
So no, I don't think Starforce is the problem. There is something else going on here. Perhaps it's unique to the Steam version of SH3. It doesn't make sense that the Steam executable would be unique, but apparently it is.