Have a good idea, and suddenly everyone tries to take advantage of it.
XBox sales ladder for Indie Games -
Top Indie Games (Full Versions purchased)
1 CastleMiner Z
3 Total Miner: Forge
4 The $1 Zombie Game
5 FortressCraft Chapter 1
6 The Impossible Game
7 Avatar Paintball
8 Avatar Deathmatch
9 Fortress Wars
Source: Xbox Live's Major Nelson LIVE Activity for week of May 7th :
So 4 out of the top 5 are wanna-be clones/spinoffs (plus Fortress Wars). XBox Minecraft is 3rd in the LIVE sales and first in the Arcade sales.