This is a legitimate question, and one that has some answers that have evolved since the original SR9 and SR40 were released.
In the original SR9, there were two options of stainless. Blackened stainless or brushed stainless.
Then when the compact was released, the only stainless option was brushed stainless. The black or "blue" as they called it, was carbon steel, or "alloy" steel as they call it. It's not stainless, but whatever proprietary finish they apply to the alloy steel, it is extremely resistant to the elements.
Now, in looking in their catalog, I do not see any of the SR series with a blackened stainless option. So if a guy really needs stainless, his only option will be in brushed stainless.
WAYNO.
P.S.
This discussion has been going on for some time. Here's a couple links to some previous investigation...
http://www.rugerforum.com/phpBB3/viewtopic.php?t=76347
http://www.rugerforum.com/phpBB3/viewtopic.php?p=741652#741652