This is Logigamer (logic+gamer, in case you couldn’t tell). It is not a random blog of randomness, but one that contains logic, gaming, or both in each post.
If you have any thoughts on what I write, be sure to leave a comment. I'll definitely respond :).
I think the answer lies in other gaming realms, with the many genres they contain. Both games use a unique concept of being able to edit and control as much of the environment as you wish, and are capable of doing. So when you look at two WWII first-person shooters, they can be very similar, but people aren't eager to call them "copies." If they were copies, or copies of copies, etc., so would Terraria be to Minecraft. And hell, Minecraft is basically an improvement upon another game, titled Infiniminer. But nobody considers (WWII themed) Call of Duty games copies of other WWII games. This applies to other game concepts too. Influencing does not equal copying.
With that, Terraria obviously has roots in Minecraft, and would not be what it is, or maybe even exist, without that which influenced it. Furthermore, the games that Minecraft and Terraria are could be even a new genre, title unspecified.
Disagree? Is Terraria a complete copy of Minecraft to you? Is Terraria completely original? Well, what's the comments for? Sound off there. Skydra out.