I saw that too, but from I was able to make out is that you can't pay for subscriptions with it, BUT any other purchases will be charged against it, just as a normal gift card. What they say is VERY misleading, IMHO. My guess is that NO gift card can be used for blogs and periodicals. Anyway, I suggest care if you buy more than Kindle books from Amazon on a regular basis.
"Browse for your favorite Kindle books. When you find what you want, click the "Buy" button, and your credit will automatically be applied to your purchase.
Once you've entered the claim code, we'll keep the balance in your account for use on future purchases, so you don't need to enter the claim code again when you place your next order, even for non-Kindle items. Please be aware that gift cards can only be used for Kindle book purchases, not blogs and periodicals."