Jeez, why wouldn't he just give it its own name and graphics, and call it a clone? Would have been perfectly legal, and brought almost as much attention.
This may just be a thin client for the multiplayer version of Minecraft, meaning it would talk to a Minecraft server but not actually simulate the world itself.
The discussion on Reddit mentioned that it's a client for a Minecraft server's "Creative" mode (free-form building). This is the mode that is playable in-browser and lacks a lot of the world modelling that is available in the regular game mode.
Coming soon? This doesn't really need an introduction... but it probably needs permission. I wasn't intending it to go live before I'd heard back from Notch.
Save him some work and prevent him from having to spend time learning Cocoa Touch instead of working on the desktop client and server? Sometimes it's better to embrace passion than to hit the auto-lawsuit button.
That's what I'm waiting to hear about. Clicking the "Buy Now" link gives me the following: "The item you've requested is not currently available in the US store."