Yeah it is the nitro. While it really doesn't affect the flavor, it may influence your perception of creaminess. If you want to get a brew with a good mouthfeel, a good thing to shoot for would be an Oatmeal Stout. In the future, I will have a nitro system for my Stouts because I just love that effect.
Event Horizon ~ A tribute to the miracle of fermentation.
Brew what you like. Do this, and you will find your inner brewer.