Theory: The Teletubbies is an elaborate treatise on advanced chemistry. Po is obviously Potassium, La-La is Lanthanum [and the rare earths generally], and I think Tinky-Winky is a new alloy of Titanium and Tungsten.
This alloy combines the lightness of titanium with the, er, heaviness of tungsten. We don't yet know what for.
My theory is hampered or possibly helped by the fact I don't know the name of the other Tellytubby. But I am applying for funding to find out.