[pretoriusB]

Citation is needed in novel and unexpected statements and conclusions. ("Extraordinary claims", etc).

Well known facts should need no citation upon an audience of educated adults.

Still, here's a secondary corroboration for you: http://online.wsj.com/article/SB1000142405297020474090457719...

[Cushman]

That you think that unsourced opinion piece constitutes "secondary corroboration" indicates that perhaps you do not, in fact, understand when citation is needed.

[pretoriusB]

Ever tried looking around you? Do you need a citation that air is important for breathing?