Its a nice rule, but...
I think air carriers around the states tend to stick more to a policy of bag match at origination, rather than bag match at connection. Since so much travel is done via hubs around these parts, connections aren't always as seamless as one may think. I've had my bags on my connecting flight, the prior connecting flight, and the next flight (despite a 3-hr weather delay at the connecting city). My guess would be that an assumption is made that if you're ticketed to pass through a hub and make the first flight, your bags are ok to go onto a flight before yours.
I've been able to use that to get routed on earlier connecting flights. I was initially told that if I had checked baggage I couldn't move to an earlier flight because passengers must remain with the luggage. I asked then if they could promise me that my luggage would stay with me on my flight rather than be loaded onto the earlier flight and be an easy target for theft as it sat around at my final destination. That elicited a rather nasty look and standby status for the earlier flight. In the end, the earlier flight was so delayed (though still earlier) that I took the later one I was ticketed on. And yes, my bags were sent on the previous flight.