I do not know about a particular set of keys that will fit all Saturns and I am sure that Saturn would not admit to it if there were.
I do know that based on my '92 Saturn, that the key that fits the door fits the ignition, and that there are a finite set of key combinations. I guess someone could go around trying their key in different Saturns but that would look odd.
I also know that there is a number that a locksmith can use to make a key without the original. I guess if someone were to jimmy the lock and look at your manual and had the locksmith equipment, they could make a key.
Probably they came along with a tow truck and stole it, that would probably arouse less suspicion.
While you could hotwire the car, it would not steer, due to the locking wheel. Unless, someone can unlock it. I have heard of people replacing the whole ignition mechanism and using their own key. I do not think it takes as long as one might imagine.
I guess it depends on the thief’s willingness to take the risks and the likelihood of being spotted in your neighborhood.