i kinda expected the habitable or non-habitable to depend more on the race itself - like humans, they're oxygen-breathers so they prefer planets that are more akin to earth and don't have a thinner, or even a more high-pressure, atmosphere. so only SOME of the nominally-habitable planets would be ideal for humans. then for another race, if they're non-oxygen-breathing, other planets would be ideal for them while the oxygen worlds would have to go through terraforming.
that's one thing i liked in MoO - not all habitable planets were good locations for specific races. it made it much more interesting and competitive to find the right planets.
EDIT: in MoO, with that system, for some beings, even the gas giants were habitable