I don't think you can really compare smartphones and ereaders regarding ease-of-touchscreen-use. I've got big fingers and I always have a hard time with the smart phones either getting them to recognize my touch or correctly pressing the right key, yet I am able to use the touchscreens on my Sonys just fine. The scope of the finger movement is much more forgiving on the ereader.
One thing I did do was pay attention to how I held the ereader with each hand and set the turn-page swipe to the direction that made the most sense for the hand positions. I swipe my pages left-to-right, rather than right-to-left, because I usually hold the ereader in my right hand and use my thumb to swipe.