Here's a more reliable source than Wiki for studying this:
http://www.cvphysiology.com/Microcirculation/M011.htm
I would also suggest an investment in a good physiology textbook if you're really serious about studying these questions. Something like Guyton's physiology if you're interested in learning it at the level med students would learn the subject.
I haven't looked at any current editions of upper level physiology texts in a long time; I'm busy spending my time finding something that students with no physics courses can understand. So, I don't know which ones are still good at presenting all of the equations and which are "dumbed down" for students who have no time for that. When I was an undergrad student (a LONG time ago), we used Berne & Levy's physiology text. If it is still the same style and caliber of text, I would not recommend buying that one, but finding it in a library and borrowing it as an extra reference. It's not very readable without a lecture to accompany it and guide you through it. But, it really went into a lot more of the physics concepts and equations used to address these issues.
Wikipedia is NOT a reliable source for science topics, unfortunately (which probably means it's flawed in a lot of other subjects too, for the same reasons). It's too easy for some student with an incomplete understanding of a subject to change things to what they think is right but is misleading or wrong.
As you read up on the subject, you will see that, indeed, there are two components of the equation that address the movement of things besides water, because just factoring in water alone would be oversimplified to the point of being useless. The oncotic forces take into account protein concentrations, and the filtration coefficient takes into account the movement of proteins or ions. The filtration will be different in different organs, because permeability of capillary beds to larger molecules, such as proteins, differs based on the functions of those organs.
