Do you know for certain that the 737-800 has replaced
the 300 on that route? Sometimes, Delta, will alternate
equipment (aircraft) when others are being serviced.
I know when the 737-800 first started service with Delta, the airline flew the aircraft into our airport,
Pensacola, FL. (PNS) a couple times. That was nearly
a year ago, and I havnt seen the airplane here sence.
The route is usually served with a 727 or MD-88, so I say all that to say that, unless you know for sure other
wise, Delta was probably just using the airplane for the
day. I would think Delta uses equipment that is
most beneficial to them and the route.