I"m not sure if I understood your question or I just didn't answer your question right. However, the earth has been bombarded by many debris floating around in the early solar system. This was due to the fact that in the belt around the sun various aggregations of material happened through mutual attraction of smaller materials, that grew. This is how all the planets formed in star systems. At a certain period in time the diverse clumped together debris where big enough to be called proto planets and the rest was still called debris or asteroids.
The theory you are mentioning is called the giant impact theory or the Theia impact. Earth was not struck by an asteroid, but by another proto planet called Theia. It is assumed that this has happening a lot, also in other star systems. The fact that from this impact the earth and the moon formed in the form they currently have, is unique in our solar system. We only see it with the earth. However, impacts between proto planets is not considered to be rare in the early solar system, so the chance that the Theia impact could happen might have been small, but considering the chance of colliding proto planets was very high, the possibility was there.
Now back to your remark that the moon has exactly the right speed to stay in orbit with the earth. This is not true. The moon actually has a speed too high to stay in orbit and the distance between the earth and the moon is getting bigger each year. High precision measurements are made and suggest that the moon is spiraling away from the earth with a speed of about 4 centimeter per year. Of there the course of the last 4 billion years, this has thus been quite a distance and it suggests the speed is not exactly right, but a bit too high.
Still, a Theia-like collision between Venus and another proto planet would not have resulted in a planet moon system, due to the tidal forces from the sun. A similar thing would apply for Mars, but here Jupiter is the reason for the absence of such a pair. The outer planets are too big and would have not resulted in material being able to escape the planet's gravity.
So, yes, the existence of the earth moon can be seen as a unique situation, but this is not because the kind of impacts didn't happen. It is because the earth was just at the right distance from the sun and Jupiter to result in such a pair. Impacts like the Theia impact were not rare. Do, however, understand that the Theia-impact is a theory that has good acceptance, but is not undoubted. There are several questions about the validity of this theory.