Sometimes N=2 is extremely different from N=1. Specifically when we have N=1 and we suspect that it might be unique, or extremely rare to the point that you wouldn't expect to find instances.
Sometimes N=2 is not that different from N=1 though. Specifically when you don't think the situation is necessarily that rare, you just don't have a big population to choose from. That's the situation here.
Astronomers expect to find other Earth-like planets. We suspect rocky planets aren't that rare, we know planets at comparable distances from the star are not that rare, and we know H20 is plentiful in space. The problem is one of detection. The smaller the planet, the harder it is to detect water, so most of what we've found so far is gassy giants.
A good analogy is the fact that I don't know anyone who shares my birthday. That doesn't mean I would be amazed if I were to find someone did share my birthday, cuz I have no reason to suspect my birthday is particularly rare. I just don't know that many people.
