Minus the resource-base difference I'd imagine the roughly same considerations applied to both the Celts and the Germans.

As for the Romans and such, I wouldn't be surprised if the simple fact of Mediterranean ecology was a major part of the difference. The Med is in many ways very different from Europe north of the mountain ranges ringing it, and that's bound to have shown in the cultures that developed there.

'Course, the Latins were on the East Med ancient high-culture orbit through the Greek colonies and similar transplants, traders and whatnot, so of course they also adopted a lot of ideas and influences from there.

As for spears, well, those are cheap, cheerful, effective, and in forested regions in particular every household has a few if only for hunting and squabbling with the neighbours. Quite well suited for materially somewhat impoverished but pugnacious tribal warriors, in other words. Much later the Vikings were so fond of spears and axes for the exact same reasons - pretty much everyone had them already for utility purposes and knew how to use them, so pressing them into war service was a perfectly natural follow-up. Which of course detracted nothing of the prestige of the very expensive swords.