I don't see that this "IS ridiculous". It may not be the policy you would choose, and I'm not saying it is the one I would choose, but that's not the same thing as calling is ridiculous. It is perfectly tenable to restrict those seats to Golds/Premiers only and not their hangers-on. (Does anyone know if the companions of Premiers can be pre-assigned those seats, incidentally?)

I actually see the policy that restricts Silvers from pre-assigning seats for a companion on a separate PNR to be rather more anomalous, since whether or not you have separate PNRs is often a bit of an accident of planning. I would understand if there were a restriction to, say, a single companion in the same cabin, but the same-PNR rule seems a bit odd, although I'm not sure I would say "ridiculous".