DrDoc - 6:34 am on Aug 19, 2013 (gmt 0)
Different forums have different rules.
How "big" a site is doesn't matter. How "relevant" it is, does. If a small site has the original source, it is likely to be linked to. The preference for some sites is also that they describe the topic in a more generic way than the original source, thereby appealing to a larger audience.