There's something special about Terraria that made it more than just another Minecraft clone...this much was already apparent with the game selling over one million copies. It looks like that number might rise, as the game is going to be seeing a boxed retail release in March, though for a substantially higher price than it's digital incarnation. The boxed version will be sold through Merge Games and right now only appears to be seeing a UK release, priced at £20. For the extra cash you'll get an exclusive in-game item, poster, trading cards and a toy pickaxe when it releases on March 16th.
This is certainly interesting, though I'm not sure how well it will perform at a higher price point. Part of the appeal was the low cost of entry I think. I guess time will tell.