The Kindle store policy is: competing venues cannot undercut Amazon on price. If a lower price gets posted, Amazon will eventually detect it (or someone narcs about it) and then they'll price match on the Kindle store.
Some authors actually exploit this policy to get Amazon to drop the price of their Kindle book below the minimum allowed. As in, making it free, which an author can't do when they upload and price their book; free is not allowed. I didn't intentionally pursue this, but I figured it was bound to happen.
About a year ago, I posted a version of Game Over on the Kindle store. This was a special edition I intended just for Kindle owners in that I added another scene amounting to 2,000 additional words. I labeled it an Extended Edition and put a 99 cent price on it. Over on Smashwords, I had the original, shorter version of Game Over for sale at no charge. I was thinking I might get a month or two before Amazon price matching kicked in. It ended up being 10 months, and no, I didn't assist the process.
But there are a healthy number of Kindle owners taking advantage of the $0.00 price since it changed last month.