I think we need to untangle a few of the concepts here because even in Tim's book, his practical advice for how to solve issues may be a bit confusing without a long background explanation. So here's the explanation:
1) Homogenization uses high pressure (20-60 MPa) to mechanically reduce the size of fat molecules. This means there are more physical molecules. At higher pressures, there is the possibility for proteins (casein) to be degraded as well, or for some of the fat to bond to the proteins.
2) Pasteurization uses heat, and even at lower (145-165F) temps, some dissolved Ca++ ions go out of solution. At higher temps, more ions go out of solution and also caseins and globulin and albumen denatures. The ions act as a sort of glue among the alpha caseins so they can bond and form curd.
3) Adding CaCl2 adds some calcium back into solution. In the case of pasteurized milk, it's necessary because those ions are bound up during pasteurization. In the case of homogenized milk, the matter is more complex. There is no single authoritative explanation in current science for why homogenized milk curd is not as firm as unhomogenized. Some explanations include that the extra fat molecules adsorb proteins, and that with more fat molecules, the integrity of the casein matrix is weakened because the gel has to accommodate more large physical molecules and therefore has fewer contact points among the casein micelles. Regardless of the mechanism, having Ca++ ions available makes for stronger bonds, meaning a firmer set.
End points are that you may or may not need CaCl2, regardless of pasteurization or homogenization. It depends on the milk. In many cases, a little bit helps. CaCl2 is sort of a fix-all, and it does the same thing -- improves bonding, but how that impacts curd differs between pasteurized and homogenized because the milk is damaged in different ways.