Most of us thought the same thing. On the day of the mishap, I was of the belief that all turbojet/turbofan airliners were certified with stopping data that did not include the use of t/r's and that they were added 'gravy'. I have since heard that that data in our onboard performance computers (OPC) for our -300s does not account for the use of reverse thrust (SWA software product). I heard that the -700s did use the effects of reverse thrust and that this is a Boeing software product. I do not know to this date if the -700 certified stopping distances use t/r effect or if they just added it to the OPC software to increase the performance perception. Perhaps a Boeing engineer or someone with an actual Boeing 737NG flight manual could enlighten us.