Staying in gear and using DFCO will slow you down much faster than coasting in neutral. You'll probably end up using more fuel if you try to pulse and glide with DFCO vs cruising at a constant speed.
The reason the RPM's stay at 2k when you let off the gas is because its a manual. Unless you do something to disconnect the engine from the wheels, like pushing in the clutch, the RPM to MPH ratio will always be the same for each separate gear no matter what you do with the brake or gas pedal. If you RPM's dropped when you let off the gas, you would have major issues.
Also, RPM's aren't a very good gauge of fuel usage.
I'm 99% sure your Civic has DFCO. My '97 did, and I see no reason why they would have gotten rid of it. One way to test it is to try turning the ignition off while doing what you think is DFCO and seeing if there is a difference in engine braking force. If there is no difference, then you have DFCO. Because some cars are more picky than others about when they'll do DFCO and to be able to feel the difference between ingnition off/on if there is one, make sure the RPM's are over 2k and you're in 1st or 2nd gear when you do the test. Be sure to be safe, too, and do it in an empty parking lot or road.