Actually, its the other way around. Fingers -> Hands -> ?Mountain -> Earth -> ?
It is? I have only played five or so levels with that tileset, and I have 32 pages of levels. Well, I hope it doesn't matter too much though. After all, it is supposed to look a little dull.
While the tileset isn't exactly overused, it's so simple and default that every time it's used, it makes you feel like, "Oh. This tileset again."
I feel this way about basically all the default tilesets. A few of them (eg 1, 9, 13) just get used massively often, and some of the others are just so weird that they can't really be used effectively, especially when put next to other tilesets (eg 16, 17, 81).