The external specs of these various chargers may not differ, but the internal quality isn't always the same. Not sure about the Kindle charger's quality, but this article helps explain some of the price difference between aftermarket chargers and the real thing:
I've found that many cheap chargers cause touchscreens to go wonky. I tried using a cheap charger at my mom's house to charge my Paperwhite and the touchscreen went crazy. Had the same experience with various chargers on my Moto Droid. If I didn't use a good charger things didn't work very well.