Well, considering that every message I've read from people who have gone into an Apple store with a cracked screen after dropping it has gotten the same "unofffical" replacement, my (unofficial) uneducated guess is that it's a sort of a unwritten Apple policy. Or maybe it is written, somewhere that they will never admit to. (Not that Apple has ever been secretive before)
Perhaps they're realizing that the glass on the iPad2 is a bit fragile, and its easier to just play this little game than to admit to a manufacturing weakness.
Apple apparently had the policy in place even before iPad 2. I dropped my iPhone 4, googled and read about Apple replacing iPhones (even before iPhone 4 came out), so that's why I brought in my smashed iPhone to a U.S. Apple store. I figured I'd probably pay for a fix, but there was a chance they'd replace for free, which they did.