EVE General Discussion

Caldari ships are, as someone pointed out above, very spartan in nature. A side product of 'get it done as cheap as possible' aswell, so they use less material. Using mainly shields for defense also means less armor bulk. There's nothing for the crew on the ships aside from quarters and their workplaces. There's not as much crew on board in the first place. Focus on electronics over brute force.

Amarr ships are designed to look and be grand. Their interiors are quite lavish with decorations and a lot of space. There's more than likely more than a few places of religious significance to keep the crew in check. Amarr ships focus much more on brute force - HUGE capacitors, massive armored bulkheads and big, big guns powered by the most powerful reactors fitted to any ship in EVE. Amarr ships are also built to last, to a degree - If a beam only needs to be 2m in diameter somewhere, they make it 4 just to be safe. Their ships are, simply, massive.

Would have to point out that Minmatar ships are even more utalitarian than Caldari ships, but the relative inefficiency of the design and construction gives more varied ship sizes. Gallente ships are somewhere between Amarr and Caldari, though more towards Amarr.