I'd have to go with Modulus, its just a fancy way of saying they're not constructed on the planet but rather teleported in to the stargate at which they appear. I think only land units could be warped in if you upgrade the gateway to a warp gate.

I'm just curious how it works... do the built units just stack in the warp gate, and once you teleport them that's it; or can you just walk into the warp gate and queue yourself up as many times as you wish... cause that'd be super cool; no more annoying transports or waiting for that arbiter to recharge... hmmm