Why different elution buffers for Protein G and Protein A chromatography? - (Jul/19/2013 )

I have come across several protocols for affinity purification of antibodies with Protein G and Protein A. In most of them 0.1M Glycin pH 3 is recommended as elution buffer for Potein G while 0.1M Citric acid buffer pH 3 is recommended for Protein A. Can anyone explain to me why this is?

-text edited by Curtis

I have seen protocols for protein G with citric acid too, but i normally just add sds-page loading dye since i do wb.