Here's the skinny:
All steamroller completes (i.e., the stock Surly steamroller built by Surly and regularly bought at your LBS) come w/ Sugino RD cranks. The chainring on these cranks (normally) sit 45mm away from the middle of the seat bar on your frame, thus giving a 45mm chainline. The Surly cogs which come stock on the complete Steamrollers are speced to work with a chairing that gives a 42.5-43.5 mm chainline.
BUT this is nothing to worry about because the Steamroller also comes with a 3/32 8-speed chain, a chain that can easily handle this deviation in chainline with no danger in the chain coming off, little to no extra wear on the cog and chainring, and little to no noise elevation (bc 3/32 chains just run quieter than the 1/8 chain on your standard track bike; and most of the noise comes from either having the chain too tight or just having noisy cogs, and Surly cogs can be noisy).