It obviously helps our observation of exoplanets if they transit their star from our point-of-view. I would guess that the chances of this alignment are better than if their orbital plane was randomly oriented. Gravitational interaction between stars, planets, and the galaxy would increase the likelihood of inter-system alignment just as moons in our system orbit their planets in general alignment of the planets orbit around the Sun. Is this the case? On the other hand, moons in our system generally formed at the same time as the planets, which would not be the case for star systems.