It doesn't matter. The show is a money-maker for Sci-Fi, and that is what determines whether a show stays on the air; ratings are incidental to that because the determine the ad prices. The difference in what they charge for say a Mac commercial at 2.1 is probably no different than what they charge at 1.8. It also has good demos, brings some long-desired acclaim to a channel with very little going for it and sells well on DVD, iTunes and will do well in syndication.
No, there is a problem. 1.8 may be high enough to keep it on the air. The problem is if it drops more. There's not much safety room below 1.8! What if 1.8 is higher than the average for this season simply because it was the premiere.
Now, I agree that we'll have to wait and see. 1.8 should be fine to keep it around. But, will the ratings stay around 1.8? That's uncertain right now.