Is a pfo just a diagnosis of exclusion for stroke/tia seeing as 25% of population have it anyway or is it a real risk and needs to be closed ?

PFO: The american academy of neurology published a guideline on this topic. You can find it here: http://www.Aan.Com/professionals/practice/pdfs/clinician_stroke_d3.Pdf in short, there is no clear benefit of surgical treatment of the pfo, compared to medical management. The details of the history matter. Consult a neurologist.

Yes and no: Yes its an exclusionary diagnosis. No real good evidence that closure is beneficial. A recent study published in new england journal of med. Noted no real benefits.