Why is zinc not considered to have a noble gas configuration? I am wondering why we say that, for example, zinc does not have a noble gas configuration?

I would like to say beforehand that this question may has its origin in a confusion about the word "shell" or "outer shell". Wikipedia states that: 


  The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons is considered to be full.


Ok, so argon is a noble gas and its configuration is: $\ce{1s^2 2s^2 2p^6 3s^2 3p^6}$. When we speak of a shell we mean the principle quantum number $n$. In this case, the highest principal quantum number is $n=3$. However, for $n=3$ there is also the $\ce{3d}$ subshell available, which is not filled by argon.

So I conclude that "filled shell" does not mean that all available subshells for a given principal quantum number (here $n=3$) have to be filled. Because the $\ce{3d}$ subshell is empty here. Instead, I conclude that "filled shell" means, that whenever we start to fill a subshell (here $\ce{3s}$ or $\ce{3p}$), they must be filled. If there is another subshell with $n=3$ available, it has to be completely empty (like $\ce{3d}$).

But when we look at zinc, we find the configuration: $\ce{[Ar] 3d^{10} 4s^2}$.

Again, for the highest principal quantum number (here $n=4$) we have a filled subshell (here $\ce{4s}$). Additionally, all shells of the $n=3$ are also filled. There is no subshell (neither for $n=3$ nor for $n=4$) which is partially occupied. So, according to the definition from Wikipedia, what is missing for zinc to be in a noble gas configuration?

Again, let me stress, that I am not asking for what a noble gas is (I know that zinc is neither a gas nor a noble gas). I am asking what I am doing wrong, when I conclude that zinc obeys the definition of a noble gas from Wikipedia?
The difference hinges on the word "valence" in "their outer shell of valence electrons is considered to be full".

That's the difference between a $\ce{1s^2 2s^2 2p^6 3s^2 3p^6}$ configuration and a $\ce{1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2}$ one. It's not just filled principle quantum numbers or filled subshells, but (un)filled valence subshells.

The definition of valence is a bit circular here. A valence subshell is one which can react to form a bond. For argon, all the valence subshells are filled because there's a substantial stability gap in adding that last $\ce{3p}$ electron and the first $\ce{4s}$ or $\ce{3d}$ electron. (If you think about potassium, the $\ce{3d}$ orbital is even less easily filled than the $\ce{4s}$ one.) That's why the $\ce{3d}$ orbital doesn't count as a "valence" orbital for Argon -- it takes too much energy to fill. Even though it has a principle quantum number of 3, it (re)acts like it has one of 4.

Contrariwise for zinc, there's a relatively small energy gap between the $\ce{4s}$, $\ce{3d}$ and $\ce{4p}$ orbitals. You probably already know this for $\ce{4s}$ and $\ce{3d}$, as they trade back and forth during the transition metals, but $\ce{4s}$ and $\ce{4d}$ are also relatively close in energy. This is part of the reason why atoms like carbon can "borrow" a $\ce{2s}$ electron to make four one-electron-donated bonds, rather than being forced to make two one-electron-donated bonds and one two-electrons-borrowed one.  

So the definition of valence orbitals doesn't depend on their quantum numbers, but on the energy required to fill them. That's why zinc is not a noble gas - the $\ce{4p}$ orbitals count as valence (reactive) orbitals for zinc even while the $\ce{4d}$ don't.