I agree with DemonSVT. Strut and spring compliments wear at the same rate, more or less, and when one side fails, the other side is likely at the end of its service life. Replacing one without the other can create unpredictable handling and lead to increased wear of the new component. That you suggest otherwise by reason of the 4-wheel indepenent suspension is highly questionable.
I'm not sure what that page says, but bmw factory service training specified that struts and springs always be replaced in pairs, both for safety, handling, and legal (CYA) purposes. I'm sure Big Jim can comment here on Ford procedures.
