what is this use of sic, i thought sic was for when you are knowingly mispelling / misusing something?

"Sic" generally means thus or therefore: http://en.wikipedia.org/wiki/Sic

If wikipedia is wrong here please correct me!

As maxerickson said, the common English use is not the literal Latin translation. "The man came crauling [sic] down the hallway." The [sic] means that the misspelling or error has been left in for some reason. Other ways to express what you intended:

Original: Real time exchangers [sic: merchants] will settle on slightly less than normal exchange rates.

Alternative: Real time exchangers (e.g., merchants) will settle on slightly less than normal exchange rates.

Alternative: Real time exchangers, such as merchants, will settle on slightly less than normal exchange rates.

This was bugging me too, so now it's fixed. Thanks!

The meaning in modern English is not the same as the Latin. It is well explained at your link!

To be clear, it does not simply mean 'thus' when it is used in English text.

It's fixed, thanks for pointing this out.