It has more to do with how many wormholes there are, and to a lesser degree the difficulty if I recall. There is something like 500 units supported by just the command station itself, and then each wormhole also counts as a guard post, so you get a larger cap from that, too. I've had significant difficulty keeping planet paths clear in most diff 7 games.
All of that said, there are a lot of new specialized AI weapons in the expansion, some of which do some similar things as far as causing extra raids (Raid Engine), or causing extra cross-planet attacks (alarm posts), or some of the future stuff which causes other various effects, more along the lines of the attrition emitter in general.