This is something that is programmed into the PCM to help lower emissions and is common on many newer vehicles. I don't like it either. Try this as a test. After you release the accelerator put the trans into neutral and watch your tach. The engine speed will not return to normal idle until you stop, hence the reason you feel poor engine braking effect. Unless you figure out how to reprogram the PCM to change this you will have to learn to live with it. I preferred the old carburetors. They returned to base idle instantly... and had great engine braking effect.
(EDIT)
The trans shifting into overdrive is also a big factor in the feeling of maintaining momentum that you are experiencing, as noted by yourself and others above. You can minimize this while driving around town by leaving your trans in "3" or "D" (not OD). I do this sometimes and it does make a big difference to me because I like to coast down before hitting the brakes. Some drivers tend to go right from the gas to the brake, and therefore never really notice the car isn't slowing down on its own.