And since germanium transistors are in almost all cases of the PNP type (AC127 is one of the exceptions to this rule) and the devices are operated in a common emitter connection, a ground positive scheme is the obvious choice.
Yes, quite right.
But at the same time it is possible to make some ground-negative circuits with some PNP transistors (even if it's technically harder, so not the obvious choice).
It could have been necessary, because it was connected to something that was already ground negative : car radio comes to my mind. Again, was it the case ? Were Philips car radios sometimes ground negative ? Or was it the case with some other devices (recorders...) ?