Since Babylon 5 was the last one to be built and we are at least certain the Babylons 4 and 5 look different, are there canonical explanations for any technology differences between the various stations?
After getting B4 mostly complete and nearly operational, only to have it vanish, Earth Alliance was on the verge of giving up.
It was only after an offer of support from the Minbari (which they used to veto commanders not named Jeffery Sinclair) that construction on B5 began - and its design is noticeably trimmed. B4 had two separate rotating sections to simulate different gravities, as well as engines that would allow it to be mobile in emergencies. Neither feature made it to B5.
Quote from the creator:
B5 is smaller than B4 because they sunk most of their budget into B4; on B5 they had to get outside funding, and scrimped.