[jswhitten]

The orbital plane of planets in a given system is random as far as we know, and not related to the plane of the galaxy. Our own solar system, for example, is tilted more than 60 degrees from the plane of the galaxy's disk.

So as you might expect, more than 99% of all planets in a sample are undetectable by this technique. Kepler has been so successful because it is watching about 150,000 stars at once, all in an area of sky that would be covered by your fist at arm's length.